B.Com. (C.A.)
Third Year
Core Paper No. 14 SOFTWARE DEVELOPMENT WITH VISUAL BASIC
BHARATHIAR UNIVERSITY SCHOOL OF DISTANCE EDUCATION COIMBATORE – 641 046
1 (Syllabus)
B.Com. (Computer Applications) – III Year
Core Paper-14 SOFTWARE DEVELOPMENT AND VISUAL BASIC
Objectives : To enable the students to develop a front end tool for Customer Interaction in Business. UNIT – I
Introduction – Client/Server – Benefits of Client/Server – Downsizing – Upsizing- Right sizing – Client/Server Models – Distributed Presentation – Remote Presentation – Remote Data – Distributed Logic – Distributed Data – Client/Server Architecture – Technical Architecture – Application Architecture – Two Tier Architecture – Three Tier Architecture OLTP & n Tier Architecture. UNIT – II
Introduction to Visual Basic – Steps in VB Application – Integrated Development Environment (IDE) – Menu Bar – Tool Bar – Project Explorer Window – Property Window – Toolbox – Properties, Methods and Events – Event Driven Programming – Working with Forms – Variables – Scope of Variables – Constants – Data Types. UNIT – III
Functions – Procedures – Control Structure : If – Switch – Select – For – While – Do While – Arrays – User Defined Data Types – Data Type Conversions – Operators – String Functions – Data and Time Functions. UNIT – IV
Creating and Using Standard Controls : Form, Label, Text box, Command Button, Check Box, Option Button, List Box, Combo Box, Picture Box, Image Controls, Scroll Bar – Drive List Box – Directory List Box – Time Control, Frame, Shape and Line Controls – Control Arrays – Dialog Boxes – Single Document Interface (SDI) – Multiple Document Interface (MDI) – Menu – Menu Editor – Menu Creation. UNIT – V
Data Controls – Data Access Objects (DAO) – Accessing and Manipulating Database – Recordset – Type of Recordset – Creating a Recordset – Modifying, Deleting Records – Finding Records – Data Report – Data Environment – Report – Designer – Connection Object – Command Object – Section of the Data Report Designer – Data Report Controls.
2 CONTENT
Lessons PAGE No. UNIT-I 1 Client Server Technology : An Introduction 4 UNIT-II 2 Introduction to Visual Basic 35 3 Integrated Development Environment (IDE) 42 4 Methods and Events 51 UNIT-III 5 Functions 72 6 Define Control Structures 81 7 Arrays 102 8 Operators 110 UNIT-IV 9 Using Standard Controls 122 10 Other Controls 141 11 Timer Controls 152 UNIT-V 12 Using Data Controls 166 13 Record Set 184 14 Data Report 193
3 UNIT - I
LESSON-1 CLIENT SERVER TECHNOLOGY : AN INTRODUCTION
1.1 INTRODUCTION
The term client/server was first used in the 1980s in reference to personal computers (PCs) on a network. The actual client/server model started gaining acceptance in the late 1980s.
The client/server software architecture is a versatile, message-based and modular infrastructure that is intended to improve usability, flexibility, interoperability, and scalability as compared to centralized, mainframe, and time sharing computing . Client/server describes the relationship between two computer programs in which one program, the client, makes a service request from another program, the server, which fulfils the request.
Although programs within a single computer can use the client/server idea, it is a more important idea in a network. In a network, the client/server model provides a convenient way to interconnect programs that are distributed efficiently across different locations. Computer transactions using the client/server model are very common. For example, to check your bank account from your computer, a client program in your computer forwards your request to a server program at the bank. That program might in turn forward the request to its own client program that sends a request to a database server at another bank computer to retrieve your account balance. The balance is returned back to the bank data client, which in turn serves it back to the client in your personal computer, which displays the information for you.
Nearly all the major online information and e-commerce services (sites such as Amazon.com, eBay, Yahoo, MSN, and more) follow the client-server file sharing model. On a smaller scale, most campus services (such as NetFiles, Express Email, Illinois Compass, and Banner) also follow the client-server file sharing model.
4 1.2 DEFINITIONS
There are a variety of definitions for the term client/server. The client/server system is defined in terms of individual pieces that work together as a whole and viewed as a system that integrates hardware, software, and networking. This integration of technology is specifically designed to share resources, in support of one or more business functions, in multiple locations simultaneously.
As an example is the Internet itself is the world’s largest client/server system. This client/server system is comprised of thousands of clients and servers transferring information and supporting millions of business functions across a network that spans the globe.
1.3 ADVANTAGES OF CLIENT/SERVER ARCHITECTURE
The client/server model is particularly recommended for networks requiring a high degree of reliability, the main advantages being: centralised resources: given that the server is the centre of the network, it can manage resources that are common to all users, for example: a central database would be used to avoid problems caused by redundant and inconsistent data improved security: as the number of entry points giving access to data is not so important server level administration: as clients do not play a major role in this model, they require less administration scalable network: thanks to this architecture it is possible to remove or add clients without affecting the operation of the network and without the need for major modification
1.4 DISADVANTAGES OF THE CLIENT/SERVER MODEL
Client/Server architecture also has the following drawbacks: increased cost: due to the technical complexity of the server a weak link: the server is the only weak ling in the client/server network, given that the entire network is built around it! Fortunately, the server is highly fault tolerant (primarily thanks to the RAID system)
1.5 CLIENT/SERVER SYSTEM OPERATION
A client/server system operates as outlined in the following diagram:
5
The client sends a request to the server using its IP address and the port, which is reserved for a particular service running on the server. The server receives the request and responds using the client IP address and port . Every client/server systems consists of at least one of each of the following:
A client that requests information; A server that supplies information; A network that transfer information between the client and the server;
The client component of the client/server system can be either hardware or software. In the hardware context, a client is the personal computer functioning as a workstation. This client workstation is capable of stand-alone information processing, which distinguishes it from its mainframe predecessor, the dumb terminal. In the software context, a client is the software that allows to interact with the information residing on the server. Web browsers are examples of software clients, as are email programs (Orifaldi 1996).
The server component can also considered both hardware and software. As hardware, the server is typically a personal computer or workstation with enhanced storage capacity.
Often, it resides in the same location as the business activity it is required to support. As software, servers have a variety of incarnations, depending on the operational function. For example, windows NT Server acts as a secure server, allowing users to share files and printers over a network. Web servers like Microsoft’s Information Server provides access to and delivery of information over the World Wide Web (Martin 1997).
1.6 MOST CLIENT-SERVER SYSTEMS HAVE THE FOLLOWING DISTINGUISHING CHARACTERISTICS
1. Service: client-server is primarily a relationship between processes running on separate machines. The server process is the provider of services. The client is a consumer of services. In essence, client-server provides a clean separation of function based on the idea of service. 2. Shared resources: a server can service many clients at the same time and regulate their access to shared resources.
6 3. Asymmetrical protocols: there is a one-to-one relationship between clients and servers. Clients always initiate the dialog by requesting a service. Servers are passively waiting on requests from the clients. 4. Transparency of location: the server is a process, which can reside on the same machine as the client or on different machine across the network. Client-server software usually masks the location of the server from the clients by redirecting the service calls when needed. 5. Mix and match: the ideal client-server software is independent of hardware or operating system software platform. One should be able to mix and match client and server platforms. 6. Message-based exchanges: clients and servers are loosely coupled systems which interact through message passing mechanism. The message is the delivery mechanism for the service requests and replies. 7. Encapsulation of services: the server is a specialist. A message tells a server what service is requested and it is up to the server to determine how to get the job done. Servers can be upgraded without affecting the clients as long as the published message interface is not changing. 8. Scalability: client-server systems can be scaled horizontally or vertically. Horizontal scaling means adding or removing client workstations with only a slight performance impact. Vertical scaling means migrating to a larger and faster server machine or multi-servers. 9. Integrity: the server code and client code is centrally maintained, which results in cheaper maintenance and the guarding of shared data integrity. At the same time, the clients remain personal and independent.
In a client/server system, the network is the glue that binds the various pieces of hardware and allows the sharing of data and information. Networks are generally considered hardware, as they provide a physical link between clients, servers, printers, and other shared resources. In addition, in cases where networks are required to link and facilitates interaction between varying vendor-specific resources, middleware may play a role in supporting network functionality.
Middleware, as the name implies, is the piece of hardware or software placed between two different technologies to allow the two technologies to interact with each other. In the context of client/server systems, middleware has a variety of incarnations;however, the two most common are: Network Middleware which handles message routing between different platforms;
Database Middleware which handles the translation of data request into database commands.
7 Client/server information systems architecture must serve three purposes: 1. Respond to the organization’s need for easy information access, flexibility, smooth administration, reliability, security and proficient application development; 2. Utilize current installations of hardware, software and networks, which often run mission-critical applications that cannot be compromised; 3. Anticipate future demands on information systems and networks;
Client/Server computing systems come under the broad category of system architectures known as “Open Systems Architecture”. In an open systems environment, hardware and software from different vendors are interchangeable and can be combined into an integrated working environment.
Two important concepts in open systems are Interoperability and Interconnectivity. Interoperability - means that open systems can exchange information meaningfully with each other even when they are from different vendors. For example, manufacturing relies on VAX/VMS, Accounting runs of the IBM 3090 mainframe, sales and marketing use. OS/2 server running Netware (Network Operating System) on a Token Ring network and top management and corporate planning need real time data from all three on their PCs and Macintoshes. Interoperability is at the software application level.
Interconnectivity - refering to the ability to connect computers from possibly different vendors, is an integral part of interoperability. Interconnectivity is at the hardware level.
1.7 CLIENT SERVER CONFIGURATION
Although the client/server idea can be used by programs within a single computer, it is a more important idea in a network. In a network, the client/server model provides a convenient way to interconnect programs that are distributed efficiently across different locations. Computer transactions using the client/server model are very common.
You can take the example of your bank account - To check your bank account from your computer, a client program in your computer forwards your request to a server program at the bank. That program may in turn forward the request to its own client program that sends a request to a database server at another bank computer to retrieve your account balance. The balance is returned back to the bank data client, which in turn serves it back to the client in your personal computer, which displays the information for you.
Client/server networking, however, focuses primarily on the applications rather than the hardware. The same device may function as both client and server; for example, Web server hardware functions as both client and server when local browser sessions are run there. Likewise, a device that is a server at one moment can reverse roles and become a client to a different server (either for the same application or for a different application).
8
What are the applications of Client/Server model? As you all know some of the most popular applications on the Internet follow the client/server design like: • Email clients • FTP (File transfer) clients • Web browsers
Each of these programs presents a user interface (either graphic- or text-based) in a client process that allows the user to connect to servers. In the case of email and FTP, the user enters a computer name (or sometimes an IP address) into the interface to set up future connections to the server process.
For example, an Earthlink subscriber enters the name smtp.earthlink.net into the configuration settings of their email client to allow them to send messages over the Internet. In the case of email, a person generally enters the server information only one time, as the server side of the connection rarely changes.
When using a Web browser, the name or address of the server appears in the URL of each request. Although a person may start a Web surfing session by entering a particular server name (such as www.yahoo.com), the name regularly changes as they click links on the pages. In the Web model, server information is provided by the HTML content developer encoded in the anchor tags.
9 Client/server systems can be configured in a variety of ways, depending on what is going to be accomplished. These different configurations are called client/server system architectures, the most common of which is the two-tier and three-tier architectures.
1.8 ADVANTAGES OF CLIENT SERVER MODEL Resource Sharing Communication GroupWare Management Control Reduced Costs - downsizing Support business environmental changes Improved Information Accessbility Faster/Better Information Open Architecture - Compatibility Issues Empowered Users
Benefits and risks
Client-server file sharing has both unique benefits and unique risks.
Benefits of client-to-server file sharing
Central administration and security: Both for system administrators and for system users, the client-server model of file sharing means that there's only one system (or group of systems) responsible for the data distribution, and usually a professional system administrator (or team of administrators) deals with the security issues.
Unlike system-native file sharing, where every user needs to be his or her own security officer and set file permissions on every share, client-side users typically don't have to change any security settings in order to access files on the server or post files for distribution from the server. The security design is taken care of by the server's administrators. Users simply need to make sure their connection to the server is secure, by using encryption methods such as SSL, SSH, and the like. Then the server sends the files (applications, web pages, etc.) over the secure connection to the client who wants the information.
NetFiles, Express Email, Illinois Compass, Banner, and many more server-based file and data sharing services automatically require users to make secure connections. If you're using any of these systems, you've already taken care of the encryption you need, because you aren't allowed to connect without it. The encryption ability may be built into your web browser, your email client, or another piece of software required for access.
10 Risks of client-server file sharing
Single target for attacks: Because a client-server model transfers most of the security responsibilities to the central server, most of the security risks focus on the server as well. If a password database is compromised, or if a file is infected with a virus, security problems can arise for the users who store their passwords in the database or download infected files. In addition, the client-server file sharing model is more vulnerable to denial- of-service attacks. Since everyone knows that the data comes from the central system, attackers can overload the system with fake requests for information and slow the system to a halt.
Not all systems are well secured: Although many systems require the use of encryption to protect your password and your communications with the server, not all systems are designed this way. Some web sites store passwords unencrypted, send them to you in unprotected email for your records, or simply assume that security isn't required. For example, many chat, blog, forum, and other noncommercial sites assume that since no money is changing hands, password security isn't as important as it would be to a bank or online store. If you reuse passwords in more than one location, a compromise of a forum password can make your other accounts vulnerable.
Downsizing
The process of moving an {application program} from a {mainframe} to a cheaper system, typically a {client-server} system.
The clear definition of downsizing are given below : 1) Converting mainframe and mini-based systems to client/server LANs.
(2) To reduce equipment and associated costs by switching to a less-expensive system.
With few exceptions, mainframe sites are either considering, or are in the midst of, downsizing from their mainframes. It is rare nowadays to find a reference to mainframes in the press that does not state that they are obsolete, expensive, and doomed to extinction in the near future. Because of this negative notion, there is much talk about downsizing from mainframes to smaller systems. Undoubtedly, there is a strong increase in the number of new applications being developed in client/server technologies. There are many situations when an IS department might develop a new application on a client/server platform.
In a 1993 survey conducted by the big-six accounting firm Deloitte & Touche and published in Computerworld, a poll of more than 400 CIOs showed that 27% of their applications were on a client/server platform, up from 5% in 1992. And, a 1994 survey conducted by the same firm on the same CIOs indicated that 43% of their applications were on a client/server platform, up significantly from 27% in 1993. The survey did not take into account the size of these applications --- but just the number of applications.
11 This survey, though, also showed a distressing conclusion. The 1993 average IS budget only rose by 0.04%. However, companies making use of client/server technologies in 1993 saw jumps of 9%. And in 1994, companies with more than 25% of applications on client/server saw jumps of 16%. What this means, according to the person who headed the study, is that “....client/server is not cheaper. When you are making a commitment to client/server, you are making a dollar commitment.”
This was no surprise to many people. For example, Rose Taylor, the general manager of planning and architecture at Chevron, said that “Many outside consultants and companies are selling client/server as the latest and greatest thing to solve all your problems.” Charles Popper, the CIO for Merck & Co., indicated that “...the dissatisfaction we’ve seen relates to the cost of client/server.” Steve Pliskin, a principal at Deloitte & Touche, articulated that “They [the industry] sold an awful lot of technology before its time.”
1.9 THE TRUE COST OF MAINFRAMES
MIPS
A large mainframe, with hardware and software, can cost between £10 to £20 million pounds. The most expensive IBM-compatible Pentium-based PC can be purchased for less than £10000 pounds. It would be naive to say that PCs are 1000 or 2000 times more productive than mainframes. What is needed is a more common yardstick of computer effectiveness by which systems of all sizes can be compared.
Processing speed, or the rate at which a computer can process instructions, is one possible measure. Dividing the cost of the computer by its MIPS rating would seem a convenient measure of effectiveness. A large mainframe running at 220 MIPS costing £8 million pounds will have a cost- per-MIPS of £36,000. A PC on the other hand, might have a cost-per-MIPS rating of £100. Clearly, in this measure the mainframe would have a disadvantage.
However, MIPS for years has stood for Meaningless Indicator of Processing Speed in our computing industry. Computers of different designs do not have the same criteria regarding which instructions should be counted in calculating MIPS ratings. And some designs have rich instruction sets, whereas RISC-based processors have a small set of simple instructions. MIPS is not a sensible measure of processing speed, even when comparing systems of similar design.
Data Handling
For most organizations, the work is data-intensive rather than processor-intensive, where relatively simple operations are applied to very large amounts of data. The calculations for producing an invoice or airline seat reservation are trivial, but a lot of data has to be retrieved, updated, and stored. Mainframes are specifically designed for data-intensive
12 work, with very sophisticated data-handling routines - nowadays performed by multiple dedicated processors in the central processing box and the peripheral devices attached to it. In practice, most mainframe shops are data rich, and MIPS poor --- that is, they control very large amounts of data with a relatively modest amount of processing power. In a survey by IBM of 807 installations, it was found that the mainframe typically had 3 gigabytes of data per MIPS, UNIX minis a fifth of a gigabyte, and a tenth of a gigabyte for PCs.
It is easy to make a case that the amount of data managed by the computer is of greater practical significance than speed at which the computer can perform a million additions or subtractions. Most organizations have massive files that need to be accessible. And by that measure, mainframes have as clear an advantage over minicomputers as minicomputers ostensibly have over mainframes in terms of MIPS.
User Effectiveness
Data handling speed is not an entirely satisfactory measure of a computer's effectiveness for an organization. What really matters is the number of users, performing whatever functions are necessary to the organization, that a computer can support with a reasonable level of service. If this criterion is accepted, then the key measure of a computer's effectiveness is the total cost per user over a reasonable span of time - say, five years.
The costs of computing can be divided into three categories: hardware, including printers, operating software, terminals. This has to include the cost of maintaining hardware over that period. applications software, including off-the-shelf packages and customized programs to allow the computer to do useful work. personnel costs associated with operating the hardware and software. This includes time wasted waiting for the computer system.
In the hardware category, we will look at numbers comparing an IBM ES/9021 and IBM ES/9021-520 (equivalent of an IBM 3090-600J) versus an HP 8XXS, running UNIX, capable of supporting 200 users. Here are the calculations for the basic hardware, software, and maintenance costs over five years for these two systems. These numbers exclude finance charges and inflation. The estimate for per user cost: IBM - £1545 to £2236; HP - £1680 to £2240 These are based on a workload of commercial applications and office systems, and assume that 60% of users are active at any time, and that each active user interacts with the computer every 45 seconds. These figures make no allowance for batch processing. Most sites use the overnight shift to reorganize files to improve on-line performance during the day. Mainframes are the undisputed masters of batch processing, while on-line networks are only active during office hours. However, due to the difficulties in quantifying batch processing in terms of effectiveness, it was decided to leave out the benefits of batch processing altogether. Besides, the concept of ‘batch’ is foreign to most client/server platforms.
13 Applications Software
For the IBM mainframe, the study used a ratio of one programmer for every ninety users. For an installation of 6690 users, that equates to a 75-member development staff, which at £25,000 a year, works out to £280 per user, or £1440 over five years.
The study concluded that it was likely that the cost for downsized platforms using packaged software would be less --- say £200 per year, or £1000 over a five-year period. Many packages are available for the mainframe also, but most large organizations, particularly those that use computers to gain a competitive advantage, regularly pay a premium for tailored software. The Japanese, in particular, are very averse to off-the-shelf software; and clearly, they have not suffered competitively as a consequence.
So in terms of application software, downsized platforms have an advantage over mainframes. However, the study based its numbers on the HP specifications that called for an user response time of 2-4 seconds, which is a common criterion for downsized platforms. Mainframes, on the other hand, are generally configured for sub-second response times. It was estimated that downsized configurations capable of supporting 50- 60 users would cost at least £2500 more per user over a five-year period. Today, even the largest client/server platform cannot support 200 concurrent on-line users with sub-second response time. IBM's marketing literature for client/server platforms classifies configurations supporting more than 25 users as ‘large systems.’ An under-figured system, although cheaper, will carry a cost penalty.
Personnel
Let’s look at personnel costs. All computers require some human supervision, except Commander Data of the starship Enterprise. The costs of running mainframes are very visible; operators and systems programmers who do nothing but administer the mainframe. Current mainframe configurations require one technician for every two mainframe MIPS, which, at an average employment cost of £30,000, suggests a total of £1.875 million in salaries for a 125-MIPS IBM mainframe to support 6690 users. That would amount to £1401 per user over a five-year period.
For downsized platforms, fewer technical staff are required because these systems do not normally operate 24 hours a day, like mainframes are expected to do. The study estimated a cost for operators of £75 per user per year, or £375 for a five-year period. However, it is estimated that one full-time specialist is required to support every 80 users in a typical client/server environment. If the specialist costs £24,000 a year to employ, this computes to a five-year cost of £1500 per user. The total cost for a downsized platform, is £1875 for the 5-year period. For PC LANs, the numbers are even worse. It is estimated that the average PC user spends two hours a week, or 25 minutes a day, either tending to the system or waiting for a response from it. KPMG Peat Marwick estimated a cost for PC support as £6212 per user for each year for support.
14 Do you really know the cost of PC support? A survey published in PC Magazine compared the actual component costs of PCs with the costs perceived by their users. The results are as follows:
Perceived % Actual % Hardware 60 20 Software 20 10 Supplies 5 5 Maintenance 5 5 Outside Help 5 15 Support 5 45
In other words, outside help and internal support cost sixteen times more than the users suspect, relative to the hardware and software. White-collar productivity in the United States, which has the world’s highest per capita penetration of PCs, increased by just 0.2% in the last decade. Japan, which has the lowest penetration of PCs of any developed country, recorded a far higher productivity growth. A study published in Information Week found:
”...[there is] a negative relationship between the proportion of users who have PCs and IS effectiveness. Highly effective IS organizations have fewer PCs per worker than ineffective ones.”
Dinosaur Study Totals
In addition to what We have summarized above, the ‘Dinosaur’ paper presented a variety of cost factors. The final totals are indicated in the table below:
Cost Range IBM Mainframes £5285 to £5973 Proprietary Minis £7306 to £7786 UNIX Minis £7180 to £7740 PCs on LANs £9400 to £15,500
As you can see, the final numbers are even more skewed towards giving mainframes the advantage over downsized platforms. In a separate study, published in the IBEX Bulletin, MIS managers were canvassed for the total cost and number of users for the different types of systems they use. This study came up with the following numbers:
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Type Cost AS/400 $6795 Proprietary Minis $6667 UNIX Minis $5000 Mainframes $4800 PC LANs $3571
The Hidden Costs of Downsizing Here are additional concerns of downsizing.
Data Integrity Mainframes have a very high level of data integrity. When a mainframe database crashes, data is restored to pre-abend state. Over 95% of mainframe crashes result in no significant data loss. Contrast this with the typical minicomputer or PC environment, where it's often left to the user to back-up before going home.
Decentralization Can your organization live with decentralized control? Downsizing is typically accompanied by de-centralizing of data. With the mainframe, there is no question about who is responsible for systems administration, data security, backup, recovery, and other data center functions. But client/server environments often have no central point of control. Client/server involves a whole new world of maintenance. Even simple tasks such as software upgrades can become nightmares without sufficient support.
Partitioning With the mainframe, applications are always placed on the server. But with client/server technologies, knowing how to partition application logic among client and server nodes can be very confusing. Typically, database-intensive logic is placed on the server, while activities requiring user interaction, such as querying and report writing, are on the client. Once your partitioning is hard-coded in this fashion, it can be very difficult to change short of a complete application rewrite.
Client/server is saddled with the mainframe. Why? The principal problem is distributed database software. It has evolved too slowly during the past decade. Distributed backup, security, and systems management compound the problem. Like it or not, corporate-wide data will remain centralized for the rest of the decade.
Staff Morale Little consideration is generally given to the IS professional’s emotional well-being, as staff can undergo trauma while transitioning to new platforms. With mainframes, you might tweak your database to suit certain situations. But that is nothing compared to the range of things you can do in the UNIX world. Every company knows the expense and frustration of hiring a competent UNIX administrator. You need someone both
16 technically competent and able to work with little supervision, two fairly difficult traits to assess in the fresh-from-college applicants who are the only ones likely to be interested in what you’re willing to pay. Those field-proven UNIX administrators seem to have lucrative consulting careers and are able to name their price. Will management be patient during the learning process? Will there be any mentors?
The new software technologies are utterly different. For instance, in procedural languages you break down work-flow and code it. With the newer object-oriented languages, you break down events and assign attributes to objects without really considering work-flow. To take a programmer from the mainframe world and into the client/server world, takes a certain amount of training, mentoring, and experience to pull off the transition. Of course, if you have solid skills, the transition should not be that difficult. But when you take that step into a new environment, you go back to the starting point. You have to understand that you will be frustrated for a while and just accept it.
New Skills and Training It is generally easy to re-train people who show that they really want to do it, but what about the others? Do you force-fit them into a new role? For many, it is either a matter of learning new client/server skills, or finding an employer who appreciates the old skills. PowerBuilder contrives an image that developing systems is just a matter of drawing screens and creating icons. Uh-uh - you still have to consider user feedback, the initial needs of a GUI style-guide, understanding object-oriented concepts such as classification and inheritance, and learning C.
Transition costs training. Here are some numbers published by Forrester Research, Inc., a Cambridge, Massachusetts consultancy. These costs include training and lost productivity:
cost to train a central IS person to learn a new infrastructure: $35,000 to $50,000 cost to train a developer to work on new platforms: $25,000 - $40,000 weeks of class time for each central IS person: 10 weeks of class time for each developer: 5 months of reduced productivity for each central IS person: 4+ months of reduced productivity for each developer: 2
And Wait! There are many other items to consider.
The Orange County Appraiser's Office, in Orlando, Florida, came up with a list of essential questions after conducting a two-year downsizing effort. These are some of the essential questions they considered:
Money-What can be spent for hardware, software, and project costs? What is the anticipated return of investment, and over what time period? File Sizes What is the size of the current databases? Will it shrink during migration?
17 Databases What impact will your prior database have on your new selection? Batch What are the batch processing time windows? Will the completely migrated system fit into these windows? OLTP Does the on-line transaction rate meet the minimum standard of performance for screen transactions, such as a half to full second response time? Printing Can mainframe benchmarks be met or exceeded? Maintenance Will costs drop from the associated mainframe platform, and by how many percent? Aim for a minimum decline of 30% as a first-year target. Network Can the network handle both the downsized and legacy systems as well? Hardware Can workstations be upgraded to the optimal 486s with eight meg of Ram? PC upgrades are perhaps not an issue to private companies, but for state governments with ever-shrinking budgets, this is a definite issue.
UPSIZING Upsizing is the term coined by Microsoft to describe the process of upgrading Microsoft Access Database to a Microsoft SQL Server. This allows to continue using Microsoft Access as a database front-end whereas the actual back-end is served by a separate local or remote SQL Server allowing much higher productivity and data volumes. Microsoft Access from the version 2000 on has a special Upsizing Wizard which facilitates the data migration to the proprietary Microsoft SQL Server. No other RDBMS are currently supported for upsizing.
Upsizing strategies There are two strategies how database can be migrated from Access to a SQL Server. 1. Using ODBC from Microsoft to get access to a remove database via ADO. 2. Using Access Projects (available in Microsoft Access 2000 and higher) which allow more "native" integration with Microsoft SQL Server. The first strategy is often seen as the first step towards complete migration on a SQL server on the stage 2[1], and can be seen as a part of the strategy 2. For peculiarities of every strategy see the table. Parameter Strategy 1 Strategy 2 Via ODBC using ADO, Native integration with Microsoft SQL Server Database somewhat slower than using Access Project (.adp), data access using access strategy 2. ADO Can be integrated with Integration Native support only for Microsoft SQL Server (almost) any RDBMS
18 Serves as database front-end with limited Serves as database front- functionality. Local tables are not allowed[2]. The role end with full features of Querries are generally transformed into database of Microsoft Access JET views, VBA code manipulating the data is Access Engine and VBA. transformed into procedures stored on server. (compare to thick client) (compare to thin client).
Performing the upsizing As any data migration procedure Microsoft Access database upsizing requires fundamental refactoring of the database structure and source code. Even though some aspects of this procedure seem to be automatized by the Upsizing Wizard, there are still many points requiring human intervention. Following changes have to be done on upsizing 1. Complete change of data access interface from DAO to ADO. 2. Substantial change of Microsoft JET SQL to Transact-SQL. 3. Substantial adaptation of object (e.g. tables, columns etc) names. 4. Reconception of the source code to optimally employ the new functionality of ADO and Microsoft SQL Server of the "upsized" solution.
RIGHTSIZING The goal of Rightsizing is to determine the right platform (microcomputer/network, Client/Server, mainframe/minicomputer) for an application. Rightsizing seeks to provide the best blend of application performance, usability, and cost containment.
Generally, the two factors to consider when Rightsizing
(1) database size (2) and the amount of user interaction. If both of these factors are large, Client/Server is the appropriate platform. If the database is large and user interaction is minimal, a mainframe/minicomputer is the appropriate platform. If the database is small and user interaction is constant, a microcomputer/network is the appropriate platform (although security and data integrity issues may effect this decision). If both of these factors are small, then it really doesn't matter. Look at existing platform availability and choose the most readily available platform.
The following Application Platform Worksheet can be used as a guideline for the selection of the Rightsize platform. It assigns weights to the database size and the user interaction, adds an optional amount for security & fault tolerance, then indicates the range of results appropriate to each platform. If the application falls within a range where two platforms overlap, then either platform can be used. Leverage the investment in existing equipment by selecting the platform that is most readily available.
19 The primary goal of Rightsizing onto the mainframe/minicomputer is to leverage existing computer resources, not to encourage the purchase of new mainframe/minicomputer equipment. Today's Client/Server hardware technology can provide performance and fault tolerance equivalent to all but the newest mainframe/minicomputers, at a fraction of the cost. Client/Server's cost efficiency make it extremely difficult to justify the purchase of a mainframe/minicomputer. The businesses that would require the type of processing power embodied in the newest mainframe/minicomputers are very, very few. The vast majority of businesses will easily accomplish their business goals with Client/Server technology.
If the Application Platform Worksheet indicates the need to purchase a mainframe/minicomputer, you should carefully review your requirements in an attempt to avoid the purchase. In the event of a miscalculation or a change in direction, Client/Server equipment can always we redistributed in a useful manner. Once a mainframe/minicomputer ceases to be useful, it is a net loss. The organizations buying used mainframe/minicomputers have become few and far between, and salvage for scrap metal is a painful way to dispose of a mainframe/minicomputer. Businesses usually discover that the Rightsizing process tends to move strategic applications from the mainframe/minicomputer onto Client/Server platforms. This migration frees expensive resources on their existing mainframe/minicomputer, allowing them to leverage their current mainframe/minicomputer investment and avoid expensive upgrades. Some businesses, after Rightsizing their strategic applications, determine that they can completely eliminate the mainframe/minicomputer, eliminating existing maintenance contracts, and actually reducing their ongoing operating expense. The initial step is to Rightsize all new applications. Their tendency towards Client/Server will ease the load on the mainframe/minicomputer, allowing its existing backlog of requests to be serviced, and heading off any expensive upgrades that would have otherwise been necessary. As the personnel gain experience with the Client/Server environment, they can start Rightsizing existing applications, with an eye towards enhancing business capabilities and reducing ongoing operating expenses. CLIENT-SERVER COMPUTING The client-server vision It is a vision of individual personal computers being used as "clients" in the client-server computing paradigm. This paradigm had its origins in local area networks where client machines and server machines cooperate much better than in traditional terminal- mainframe networks. Local area networks may be 1,000 times faster than terminal- mainframe networks and this fact alone facilitates tighter integration. At such speeds, information can be easily distributed between client machines and server machines and yet be presented coherently without delay or without end-user knowledge of the network topology. Client machines in local area networks can be server machines, and server machines can be clients, interchangeably. Every machine in the network has client and server qualities.
20 The Gartner Group has defined five different styles of client-server computing. [1] The difference in these styles depends on the portion of the computing process that is "distributed" to an alternate computer over the network. The five styles are defined in relation to the three main processes in a computerized application: (1) presentation (user interface), (2) process (application logic) and (3) data storage (data management) The dotted lines represent the different areas for breaking processes between the client and server machines. There are five dotted lines, each representing another style of client-server computing.
FIVE STYLES ARE : 1. Distributed presentation, also known as "screen scraping," for example, when you take a 3270 screen and dress it up with a graphical user interface front end. 2. Remote presentation, when the presentation is fully disconnected from the application logic. 3. Distributed logic, known variously as cooperative processing, peer- to-peer processing, or remote procedure calls. 4. Remote data management, which may be implemented as SQL commands, sockets, or remote procedure calls. 5. Distributed database, a logical database distributed over multiple hardware platforms. Conceptually, client-server computing is not difficult to understand, just to implement. The implementation challenges are greater as you move up the diagram from distributed presentation to distributed database.
Client-server computing is attractive because it allocates more than one computing machine to a particular task. Imagine, if you will, the difference between a terminal- mainframe application with one computer and sixty users, and a client-server application with the same number of users but sixty-one computers (sixty personal computers for the users and one computer for the server). In place of monolithic computing cycles on a centralized mainframe, client-server computing shares out computing cycles to a network of client machines and server machines.
21 1.10 CLIENT SERVER ARCHITECTURE
Components of the client server computing can be grouped into four categories of architecture. Business solutions architecture Application architecture Platform architecture Technical architecture
Now we discuss application architecture briefly
Application architecture Application architecture layer can be defined here as those services that perform business functions on the computer. It represents the components that provide the automation support for a business function or activity in the business process (but does not include the platform and cross application architecture). Fro example a manufacturer’s sales and marketing system application architecture could include sales tracking application and the distributed data architecture to support both networked sales offices and mobile sales people.
TECHNICAL ARCHITECTURE Because of its relative importance in client/server implementations .The technical architecture consists of the infrastructure and systems software layers. Discussed previously the differentiation between them is primarily a question of make to buy that is a key decision for organizations intent on” building an architecture is how much they want to build Vs. how much they simply buy from preexisting sources. An organization can choose to build a great deal, thereby making the architecture very close to what it wants. That means that there is a great deal of logic being built by the shop.
The organization can choose to buy most of what it wants. To extent that business or application demands make it necessary for the tools to be integrated, developers can then do simple assembly, or gluing together, of the pieces. The decision for most organizations depends on balancing demands. On the other hands the organization has a large front-end commitment to build and an ongoing commitment to maintain infrastructure architecture; on the other hand the organization has a tool that is exactly what it wants.
Over the years there has been a tendency to buy rather than make. This is especially the case as the market matures with more technical entrants. By purchases rather building they can then more easily apply their strong skills in the application architecture business
22 COMPONENTS OF A TECHNICAL ARCHITECTURE
Business solutions
Application Architecture
Infrastructure Technical Architecture System software
Platform
Execution development operations Architecture Architecture Architecture
An execution architecture describes the components required when an application executes. An development architecture describes the components required to create the execution architecture. An operations architecture describes the components required to operate and mange the system. These architectures must be flexible enough to accommodate a wide range of technologies, but they must be also be structured enough to provide valuable guidelines and ensure that interoperability is available where it is required.
1.11 TYPES OF ARCHITECTURE
When considering a move to client/server computing, whether it is to replace existing systems or introduce entirely new systems, practitioners must determine which type of architecture they intend to use. The vast majority of end user applications consist of three components: presentation, processing, and data. The client/server architectures can be defined by how these components are split up among software entities and distributed on a network. There are a variety of ways for dividing these resources and implementing client/server architectures. This paper will focus on the most popular forms of implementation of two-tier and three-tier client/server computing systems.
23 2-Tier and 3-Tier Client/Server Architectures Every client/server application contains three functional units: Presentation logic or user interface (for example, ATM machines) Business logic (for example software that enables a customer to request an account balance) Data (for example, records of customer accounts) These functional units can reside on either the client or on one or more servers in your application. Which of the many possible variations you choose depends on how you split the application and which middleware you use to communicate between the tiers.
Figure 1 –client server with multi level Two-tier Architecture Although there are several ways to architect a two-tier client/server system, we will focus on examining what is overwhelmingly the most common implementation. In this implementation, the three components of an application (presentation, processing, and data) are divided among two software entities (tiers): client application code and database server (Figure 2). A robust client application development language and a versatile mechanism for transmitting client requests to the server are essential for a two tier implementation. Presentation is handled exclusively by the client, processing is split
24 between client and server, and data is stored on and accessed via the server. The PC client assumes the bulk of responsibility for application (functionality) logic with respect to the processing component, while the database engine - with its attendant integrity checks, query capabilities and central repository functions - handles data intensive tasks. In a data access topology, a data engine would process requests sent from the clients. Currently, the language used in these requests is most typically a form of SQL. Sending SQL from client to server requires a tight linkage between the two layers. To send the SQL the client must know the syntax of the server or have this translated via an API (Application Program Interface). It must also know the location of the server, how the data is organized, and how the data is named. The request may take advantage of logic stored and processed on the server which would centralize global tasks such as validation, data integrity, and security. Data returned to the client can be manipulated at the client level for further sub selection, business modeling, "what if" analysis, reporting, etc.
Figure 2 - Data Access Topology for two-tier architecture. Majority of functional logic exists at the client level In 2-tier client/server applications, the business logic is buried inside the user interface on the client or within the database on the server in the form of stored procedures. Alternatively, the business logic can be divided between the client and server. File servers and database servers with stored procedures are examples of 2-tier architecture. 2-tier architecture is used to describe client/server systems where the client requests resources and the server responds directly to the request, using its own resources. This means that the server does not call on another application in order to provide part of the service.
25 The most compelling advantage of a two-tier environment is application development speed. In most cases a two-tier system can be developed in a small fraction of the time it would take to code a comparable but less flexible legacy system. Using any one of a growing number of PC-based tools, a single developer can model data and populate a database on a remote server, paint a user interface, create a client with application logic, and include data access routines. Most two-tier tools are also extremely robust. These environments support a variety of data structures, including a number of built in procedures and functions, and insulate developers from many of the more mundane aspects of programming such as memory management. Finally these tools also lend themselves well to iterative prototyping and rapid application development (RAD) techniques, which can be used to ensure that the requirements of the users are accurately and completely met. Tools for developing two-tier client/server systems have allowed many IS organizations to attack their applications backlog, satisfying pent-up user demand by rapidly developing and deploying what are primarily smaller workgroup-based solutions. Two-tier architectures work well in relatively homogeneous environments with fairly static business rules. This architecture is less suited for dispersed, heterogeneous environments with rapidly changing rules. As such, relatively few IS organizations are using two-tier client/server architectures to provide cross-departmental or cross-platform enterprise-wide solutions. Since the bulk of application logic exists on the PC client, the two-tier architecture faces a number of potential version control and application re-distribution problems. A change in business rules would require a change to the client logic in each application in a corporation's portfolio which is affected by the change. Modified clients would have to be re-distributed through the network - a potentially difficult task given the current lack of robust PC version control software and problems associated with upgrading PCs that are turned off or not "docked" to the network. System security in the two-tier environment can be complicated since a user may require a separate password for each SQL server accessed. The proliferation of end-user query tools can also compromise database server security. The overwhelming majority of client/server applications developed today are designed without sophisticated middleware technologies which offer increased security. Instead, end-users are provided a password which gives them access to a database. In many cases this same password can be used to access the database with data-access tools available in most commercial PC spreadsheet and database packages. Using such a tool, a user may be able to access otherwise hidden fields or tables and possibly corrupt data. Client tools and the SQL middleware used in two-tier environments are also highly proprietary and the PC tools market is extremely volatile. The client/server tools market seems to be changing at an increasingly unstable rate. In 1994, the leading client/server tool developer was purchased by a large database firm, raising concern about the manufacturer's ability to continue to work cooperatively with RDBMS vendors which compete with the parent company's products. The number two tool maker lost millions and has been labeled as a takeover target. The tool which has received some of the
26 brightest accolades in early 1995 is supplied by a firm also in the midst of severe financial difficulties and management transition. This kind of volatility raises questions about the long-term viability of any proprietary tool an organization may commit to. All of this complicates implementation of two-tier systems - migration from one proprietary technology to another would require a firm to scrap much of its investment in application code since none of this code is portable from one tool to the next.
3- TIER ARCHITECTURE
In 3-tier client/server applications, the business logic resides in the middle tier, separate from the data and user interface. In this way, processes can be managed and deployed separately from the user interface and the database. Also, 3-tier systems can integrate data from multiple sources. In 3-tier architecture, there is an intermediary level, meaning the architecture is generally split up between: 1. A client, i.e. the computer, which requests the resources, equipped with a user interface (usually a web browser) for presentation purposes 2. The application server (also called middleware), whose task it is to provide the requested resources, but by calling on another server 3. The data server, which provides the application server with the data it requires
27 Figure 3 - Three Tier Architecture. Most of the logic processing is handled by functionality servers. Middle-tier code can be accessed and utilized by multiple clients The three tier architecture (Figure 3) attempts to overcome some of the limitations of the two-tier scheme by separating presentation, processing, and data into separate, distinct software entities (tiers). The same types of tools can be used for presentation as were used in a two-tier environment, however these tools are now dedicated to handling just the presentation. When calculations or data access is required by the presentation client, a call is made to a middle tier functionality server. This tier can perform calculations or can make requests as a client to additional servers. The middle tier servers are typically coded in a highly-portable, non-proprietary language such as C. Middle-tier functionality servers may be multi-threaded and can be accessed by multiple clients, even those from separate applications. Although three-tier systems can be implemented using a variety of technologies, the calling mechanism from client to server in such as system is most typically the remote procedure call or RPC. Since the bulk of two-tier implementations involve SQL messaging and most three-tier systems utilize RPCs, it is reasonable to examine the merits of these respective request/response mechanisms in a discussion of architectures. RPC calls from presentation client to middle-tier server provide greater overall system flexibility than the SQL calls made by clients in the two-tier architecture. This is because in an RPC, the requesting client simply passes parameters needed for the request and specifies a data structure to accept returned values (if any). Unlike most two-tier implementations, the three tier presentation client is not required to "speak" SQL. As such, the organization, names, or even the overall structure of the back-end data can be changed without requiring changes to PC-based presentation clients. Since SQL is no longer required, data can be organized hierarchically, relationally, or in object format. This added flexibility can allow a firm to access legacy data and simplifies the introduction of new database technologies.
28 In addition to the openness stated above, several other advantages are presented by this architecture. Having separate software entities can allow for the parallel development of individual tiers by application specialists. It should be noted that the skill sets required to develop c/s applications differ significantly from those needed to develop mainframe- based character systems. As examples, user interface creation requires an appreciation for platform and corporate UI standards and database design requires a commitment to and understanding of the enterprise's data model. Having experts focus on each of these three layers can increase the overall quality of the final application. The three tier architecture also provides for more flexible resource allocation. Middle-tier functionality servers are highly portable and can be dynamically allocated and shifted as the needs of the organization change. Network traffic can potentially be reduced by having functionality servers strip data to the precise structure required before distributing it to individual clients at the LAN level. Multiple server requests and complex data access can emanate from the middle tier instead of the client, further decreasing traffic. Also, since PC clients are now dedicated to just presentation, memory and disk storage requirements for PCs will potentially be reduced. Modularly designed middle tier code modules can be re-used by several applications. Reusable logic can reduce subsequent development efforts, minimize the maintenance work load, and decrease migration costs when switching client applications. In addition, implementation platforms for three tier systems such as OSF/DCE offer a variety of additional features to support distributed application development. These include integrated security, directory and naming services, server monitoring and boot capabilities for supporting dynamic fault-tolerance, and distributed time management for synchronizing systems across networks and separate time zones. There are of course drawbacks associated with a three tier architecture. Current tools are relatively immature and require more complex 3GLs for middle tier server generation. Many tools have under-developed facilities for maintaining server libraries - a potential obstacle for simplifying maintenance and promoting code re-use throughout an IS organization. More code in more places also increases the likelihood that a system failure will effect an application so detailed planning with an emphasis on the reduction/elimination of critical-paths is essential. Three tier brings with it an increased need for network traffic management, server load balancing, and fault tolerance.
COMPARING TWO AND THREE TIER DEVELOPMENT EFFORTS
2-tier architecture is therefore a client-server architecture where the server is versatile, i.e. it is capable of directly responding to all of the client's resource requests. In 3-tier architecture however, the server-level applications are remote from one another, i.e. each server is specialised with a certain task (for example: web server/database server). 3-tier architecture provides:
29 A greater degree of flexibility Increased security, as security can be defined for each service, and at each level Increased performance, as tasks are shared between servers Time to deployment is forecast in overall systems delivery time, not man hours. According to a Deloitte & Touche study, rapid application development time is cited as one of the primary reasons firms chose to migrate to a client/server architecture. As such, strategic planning and platform decisions require an understanding how development time relates to architecture and how development time changes as an IS organization gains experience in c/s.
Figure 4 - Initial Development Effort Figure 4 shows the initial development effort forecast to create comparable distributed applications using the common two tier and three tier approaches discussed above. The three tier application takes much longer to develop - this is due primarily to the complexity involved in coding the bulk of the application logic in a lower-level 3GL such as C and the difficulties associated with coordinating multiple independent software modules on disparate platforms. In contrast, the two-tier scheme allows the bulk of the application logic to be developed in a higher-level language within the same tool used to create the user interface.
30 Figure 5- Subsequent Development Efforts Subsequent development efforts may see three-tier applications deployed with greater speed than two tier systems (Figure 5). This is entirely due to the amount of middle-tier code which can be re-used from previous applications. The speed advantage favoring the three-tier architecture will only result if the three-tier application is able to use a sizable portion of existing logic. Experience indicates that these savings can be significant, particularly in organizations which require separate but closely related applications for various business units. Re-use is also high for organizations with a strong enterprise data model because data-access code can be written once and re-used whenever similar access needs arise across multiple applications. The degree of development time reduction on subsequent efforts will grow as an organization deploys more c/s applications and develops a significant library of re-usable, middle-tier application logic.
Figure 6 - Client Tool Migration Figure 6 makes the important case for code savings when migrating from one client development tool to another. It was stated earlier that client tools are highly proprietary and code is not portable between the major vendor packages. The point was also made that the PC tools market is highly volatile with vendor shake outs and technical "leapfrogging" common place. In a two-tier environment, IS organizations wishing to move from one PC- based client development platform to another will have to scrap their previous investment in application logic since most of this logic is written in the language of the proprietary tool. In the three-tier environment this logic is written in a re-usable middle tier, thus when migrating to the new tool, the developer simply has to create the presentation and add RPC calls to the functionality layer. Flexibility in re-using existing middle-tier code can also assist organizations developing applications for various PC client operating system platforms. Until recently there were very few cross-platform client tool development environments and most of today's cross- platform solutions are not considered "best-of-breed". In a three-tier environment the middle tier functionality layer can be accessed by separate client tools on separate platforms. Coding application logic once in an accessible middle tier decreases the overall development time on the cross-platform solution and it provides the organization greater flexibility in choosing the best tool on any given platform.
31 SUMMARY In the early 1980's, ANSI, in conjunction with the University of Minnesota, defined a three layer architecture for building portable systems. This architecture divided data processing into presentation, processing (functionality logic), and data. This paper has considered the role of each of these data processing layers within the framework of two popular client/server architectures. Two tier architectures group the presentation with most of the non-database processing in a single client application. The robustness and ease of use of two tier development tools dramatically decrease initial development time, however IS organizations may pay a penalty when trying to update functionality simultaneously in a variety of systems, when trying to integrate systems, or when trying to migrate from a proprietary development tool. Three tier architectures split these three layers into three distinct software entities. This architecture requires more planning and support, but can reduce development and maintenance costs over the long term by leveraging code re-use and flexibility in product migration. Three tier architectures are also the most vendor-neutral of the architectures considered and thus can facilitate the integration of heterogeneous systems. Kean (1991) pointed out that a firm's long term ability to compete is directly related to (enabled or limited by) the reach and range provided by the firm's technical architecture. His suggestions for defining a platform include selecting architectures which: * protect existing IT investments * ensure the firm's ability to adopt new technologies * provide integration of heterogeneous resources * accommodate emerging standards embraced by a broad base of firms. Our discussion of popular client server architectures exposes the weaknesses in the overwhelming majority of current client/server systems - systems employing a two-tier architecture - as they relate to Kean's platform selection criteria. Such systems may provide adequate work group-level systems which can be developed rapidly and employ empowering interfaces. However, such systems lack the openness, flexibility, scalabilty, and integration provided by three-tier systems. The case for deploying three-tier systems will develop over time as tools mature and momentum for vendor-neutral standards increase. A variety of research opportunities exist including examining issues in migration from two-tier to three-tier systems, operationalizing the conceptual graphs presented here as they relate to development time, and studying how the level of complexity in three-tier systems acts as a barrier to its wide-spread acceptance.
32 1.12 ONLINE TRANSACTION PROCESSING (OLTP)
Distributed Computing can be categorized by two principal parts: Decision Support Systems (DSS) and On-Line Transaction Processing (OLTP) . On one side DSS means that data is mined for trends , quick answers, and summaries. It is less demanding of resources than OLTP. On the other hand, OLTP means the distributed system must deliver fast, secure, reliable, and scalable results
What is OLTP? It refers to a class of programs that facilitate and manage applications for data entry or retrieval on a computer network. OLTP systems handle active data instantly. OLTP has the capacity to ensure that multiple transactions are processed accurately and efficiently. Those using this application include banks, airlines, mail-order firms, manufacturers and retailers.
What are its applications? Applications that use this technology include sales order processing, inventory, accounts payable and e-commerce. When you withdraw money from an ATM or punch in a time clock, OLTP works behind the scenes to make the system store and manage all these transactions in real-time. The response from an OLTP system is immediate. Large applications depend on transaction management software such as Customer Information Control System to process thousands or millions of updates to OLTP-oriented databases. As the records are entered, the database is updated and the OLTP system sends a confirmation—all at the same time. Demands on such software are high as they have to function reliably 24x7x365 on dependable computer and network systems.
What is the technology powering OLTP? OLTP adopts a client-server or multi-tier computing model. The data updating mechanism allows branches to operate offline and connect to it at intervals to update or retrieve information. It can also work in an always-connected mode. The server has three components—a hardware platform, operating system and transactional engine. As the technology can work in online/offline mode, it can compensate for link failures and host downtime. The software does not permit two users to change data at the same time. Also, it does not allow a user to change information when it is being accessed by another user until the first user finishes accessing the said information. Commonly-used offline processing transaction processing facility sites use IBM’s Multiple Virtual Storage and Virtual Machine operating systems. What is the role of middleware in OLTP? Transaction Processing Software uses middleware to handle infrastructural functions such as sending data or a message from one PC to another or queuing them. OLTP is a three- tier architecture system. A three-tier system consists of a client, application server that acts as the middleware, and the database server. It enables higher processing speed to access multiple databases. Some of the examples of middleware are BEA Tuxedo’s /WS and ATMI, Encina’s Transactional RPS, and IBM’s WebSphere XD.
What are its benefits and limitations?
In an OLTP, the transactions that take place either succeed or fail it is not left incomplete. A major benefit is that when a transaction is taking place it does not affect other transactions taking place simultaneously. Along with the numerous advantages of using OLTP there are some limitations too. They are configuration and version management, and difficulty in distribution of the new updated version of OLTP or the application code patches. It should be ensured that both the new version and the patches are loaded on every machine. Performance may be affected if a client server system sends in a large amount of traffic across a network. In OLTP, latency—which is the amount of time needed to complete a single operation—and throughput often clash.
34 UNIT - II Lesson – 2 1.1 Introduction to visual basic 1.1.1 Steps in Visual Basic application 1.1.2 Creating A Project In Visual Basic 1.2 The Parts Of A Visual Basic Project Lesson – 3 2.1 Integrated Development Environment (IDE) 2.2 Menu bar 2.3 Tool bar 2.4 Form Window 2.5 Project Explorer Window 2.6 Property Window 2.7 From Layout Window 2.8 Tool box 2.9 The form designers and Code window 2.10 Help in Visual basic Lesson - 4 3.1 Methods and events 3.2 Event Driven programming 3.3 Working with forms 3.4 Variables 3.5 Scope of variables 3.6 Constants 3.7 Data types
LESSON-2 INTRODUCTION TO VISUAL BASIC
2.1 INTRODUCTION TO VISUAL BASIC
While programming in high level languages like BASIC, Fortran, Pascal, C etc, the programmer needs to know the sequence of operations to be performed by the program. The program lines are added in the same sequence.
While programming in visual basic the application developer must decide how the application interacts with the user. The user may click the mouse on various controls, or press a key or key combination on the user interface. These are known as events. The application developer must developer must decide how the application must react to the user’s actions. This is called event- driven programming.
35 In Visual basic, the application does not determine the flow. Instead, the events caused by the user determine the flow of the application. The applications are to be programmed to react to various external conditions known as events. In this way, the visual basic application, the user’s action determines the application’s flow.
In name visual basic the word “Visual “refers to the method used to create the Graphical User Interface (GUI). Rather than writing numerous lies of code to describe the appearance and location of interface elements, pre-built objects are simple added into place on screen. The word “Basic” refers to the BASIC (Beginners All purpose Symbolic Instruction Code) language, a language used by more programmers than any other language in the history of computing.
Visual basic has evolved from the original BASIC language and now contains several hundred statements, functions, and keyword, many of which related directly to the windows GUI. Beginners can create useful application by learning just a few of the keywords, yet the power of the language allows professionals to accomplish anything that can be accomplished using any other Widows programming languages.
It’s no secret that Visual Basic is the favorite programming environment of many programmers. When Visual Basic first appeared, it created a revolution in Windows programming, and that revolution continues to this day. Never before had Windows programming been so easy just build the program you want, right before your eyes, and then run it. Visual Basic introduced unheard-of ease to Windows programming and changed programming from a chore to something very fun.
Visual Basic, including how to create Visual Basic projects and seeing what is in such projects. We have also get an overview of essential Visual Basic concepts like forms, controls, events, properties, methods, and so on. And examine the structure of a Visual Basic program, taking a look at variables, variable scope, and modules. In other words, we re going to lie bare the anatomy of a Visual Basic program.
Visual basic introduced in the year 1991 by windows application. The term Visual refers to Object and basic refers to codings. Visual basic follows that “A picture is worth a thousand words”. In early days DOS is used for programming. Then they introduced the following concepts for user convince
GUI based application called Graphical User Interface. It is a user friendly. No need to create methods and functions. Build in function can be used easily. Multiple windows can execute at a time The requirements for Visual basic are Pentium with 166 mhz, 32 mb Ram and 300 mb space in hard disk to install.
36 2.1.1 Steps in Visual Basic application
Visual basic (VB) is one component of the Microsoft Studio. Visual basic can be started by using the following steps. Click the Start button 1. Choose programs b Microsoft Visual studio 6.0 b Microsoft Visual basic 6.0 Alternatively, if one is using only visual basic straight away a click on Program b Microsoft Visual basic 6.0 or double click on the Visual basic icon exist in your desktop. After Visual basic is started, the new project dialog box will appear as
The following options are available
New Existing Recent Don’t show this dialog in the future
1. New - This tab enables the creation of a new project or application choosing from an assortment to templates or wizards. 2. Existing - This tab enables the selection of an existing project displays a windows file open dialog box.
37 3. Recent - This tab lists the visual basic projects that have been used recently. 4. Don’t show this dialog in the future check box - Selecting this option will prevent this dialog box from being displayed when visual basic is started in the future. However, from the File b new project menu option, one will not receive the Existing and Recent tabs.
Whenever a project is opened or a new project is started the visual basic 6.0 Integrated Development Environment (IDE) window will appear as follows. The IDE window consist of following different parts of window.
1. Form Window 2. Toolbox 3. Project explorer 4. Property window 5. Form layout window
38 In order to see the different parts of the IDE, a new standard EXE project is created by selecting standard Exe in the new project dialog box. This will open a new project named as project1. Visual basic is now waiting for you to start the work on this new project.
2.1.2 Creating A Project In Visual Basic
There are three different editions of Visual Basic: 1. The Learning Edition, which is the most basic edition. This edition allows you to write many different types of programs, but lacks a number of tools that the other editions have. 2. The Professional Edition, designed for professionals. This edition contains all that the Learning Edition contains and more, such as the capability to write ActiveX controls and documents. 3. The Enterprise Edition, which is the most complete Visual Basic edition. This edition is targeted towards professional programmers who may work in a team and includes additional tools such as Visual SourceSafe, a version-control system that coordinates team programming.
We ll use the Enterprise Edition in this book, so if you have either of the other two editions, we might occasionally use something not supported in your Visual Basic edition. We ll try to keep such occurrences to a minimum.
The following are the some of the project types that Visual Basic supports:
Standard Windows EXE programs ActiveX EXE files ActiveX DLLs ActiveX controls Programs written by the Visual Basic Application Wizard Data projects IIS (the Microsoft Internet Information Server) applications Visual Basic add-ins ActiveX document DLLs ActiveX document EXE files DHTML applications VB Enterprise Edition controls
39 This list of project types indicates some of the ways Visual Basic has grown over the years In this case; we just want to take a look at the basics of a standard Visual Basic project, so double-click the Standard EXE item in the New Project dialog box, opening Visual Basic Integrated Development Environment (IDE).
2.2 THE PARTS OF A VISUAL BASIC PROJECT
Projects can become quite advanced in Visual Basic, even containing subprojects of different types. From a programming point of view, however, standard Visual Basic projects usually contain just three types of items: global items, forms, and modules are displayed in following diagram.
The parts of a Visual Basic project.
1. Forms
Forms are familiar to all Visual Basic programmers, of course they re the templates you base windows on. Besides standard forms, Visual Basic also supports Multiple Document Interface (MDI) forms.
Visual Basic project
Global Items
Forms Forms Forms
Module Module Module
2 . Modules
Modules are collections of code and data that function something like objects in object- oriented programming (OOP), but without defining OOP characteristics like inheritance, polymorphism, and so on. The point behind modules is to enclose procedures and data in a way that hides them from the rest of the program. Here we cover Visual Basic
40 programming techniques and style; breaking a large program into smaller, self-contained modules can be invaluable for creating and maintaining code.
The user can think of well-designed modules conceptually as programming objects; for example, you might have a module that handles screen display that includes a dozen internal (unseen by the rest of the program) procedures and one or two procedures accessible to the rest of the program. In this way, the rest of the program only has to deal with one or two procedures, not a dozen.
Besides modules, Visual Basic also supports class modules. Programming with class modules will bring us much closer to true OOP programming.
3. Global Items
Global items are accessible to all modules and forms in a project, and you declare them with the Public keyword. However, Microsoft recommends that you keep the number of global items to an absolute minimum and, in fact, suggests their use only when you need to communicate between forms. One reason to avoid global variables is their accessibility from anywhere in the program; while you re working with a global variable in one part of a program, another part of the program might be busy changing that variable, giving you unpredictable results.
41 LESSON-3 INTEGRATED DEVELOPMENT ENVIRONMENT (IDE)
3.1 Integrated Development Environment (IDE) 3.2 Menu bar 3.3 Tool bar 3.4 Form Window 3.5 Project Explorer Window 3.6 Property Window 3.7 From Layout Window 3.8 Tool box 3.9 The form designers and Code window 3.10 Help in Visual basic
3.1 INTEGRATED DEVELOPMENT ENVIRONMENT (IDE)
The Visual basic development environment includes an assortment of menus, toolbars, windows and other tools that help to create applications as quickly and as easily as possible. This group of tools is collectively called the Integrated Development Environment (IDE).
The visual basic IDE has three distinct states 1. Design 2. Run 3. Debug
The IDE consist of following types
Menu bar The toolbar Form Window Project explorer Property window Form layout window Toolbox The form designers The code window
42 3.2 THE MENU BAR
The term menu is nothing but the available option are put into group under the common name called menu name. Like the same that in Vb menu also consist of various options exist in application. The following are the types of menu exist in vb for some process.
File b File handling and printing the applications Edit b Standard editing functions, undo option exist. View b Displays or hides the windows and toolbars. Project b Sets project properties, adds/removes forms and modules, and adds/removes references and components Format b Aligns or sizes controls Debug b Starts/stops debugging and stepping through programs Runb Starts a program, or compiles and starts it Tools b Adds procedures, starts the Menu Editor, sets IDE options Add-Ins b Add-in manager, lists add-ins like Application Wizard and API Viewer Window b Arranges or selects open windows Help b Handles Help and the About box
Note: The one important job of the File menu is to create EXE files for your program. When you run a program from the Run menu, no EXE file is created; if you want to run the program outside of Visual Basic, you must create that EXE file, and you do that with the File menu s Make ProjectName.exe
3.3 THE TOOLBAR
The main toolbar, you can also display other dockable toolbars in Visual Basic: the Debug, Edit, and Form Editor toolbars. To display one of these toolbars, just select it using the Toolbars item in the View menu; the toolbar appears free – floating at first, but can dock it as you like in the IDE.
Note : If you are not sure what a particular tool in the toolbar, move the mouse pointer over the tool , the complier will show the tool tip as a message.
The visual basic standard toolbar displays different buttons and changes its appearance as one uses the different features of visual basic. One can also dock or undock the toolbars. Docking refers to the features by which the toolbox is connected or placed in a window where it works best for the users.
43 Visual basic has four default toolbars that can be made to appear on the screen or hidden using View b Toolbars menu selection. These fout types of toolbars are
1. Standard
2. Edit
3. Debug
4. Form Editor
The different toolbars are described below:
Standard b This is the default toolbar that can be seen at the top of the screen Edit b This toolbar contains items to assist in editing Visual basic code. Debug b This toolbar contains items to assist in finding errors in the code during a debugging session. Form editor b This toolbar assists in adjusting items on the forms.
3.4 THE FORM WINDOW
The form window is used to design the different forms as application will contain. An application can have one or more forms, and each form can have many controls that perform various functions. The form window can be resized to whatever size that is required. As it is resized, its new size will be displayed in the right most coordinate section of the standard toolbar. The form window is a part of the IDE window.
44 3.5 PROJECT EXPLORER
View Object Toggle folder View Code button
The project explorer is usually located at the far right of the screen. It contains a widow explorer like tree view of all the customizable forms and general code that make up your application. Each project can have multiple forms and code that activates the controls on a form is stored with the forms in separate files.
The project explorer window is viewed to manage the various components or files of the project. Related items are listed together in a tree listing the above diagram. The three buttons on the project explorer window enables the display of the code or the object (commonly the form), or the toggle the folders setting to group or ungroup the related objects. Although the project explorer window can displays the various projects, forms, modules, class modules, user controls, user documents, and property pages for an application, one will be working on only forms and code modules.
45 3.6 PROPERTY WINDOW
The properties window enables one to change one or more properties for the currently selected object. The highlighted object is usually a form or control. The various properties of an object can be viewed either in alphabetical order or by category. For example when the first text box control is placed on a form, its name property is set to Text1 by default. The properties window can be used to change this property to an appropriate name such as txtCustomer.
Most programmers reconfigure their workspace to make the properties window larger than the default to quickly access the various items in the properties window. The method of changing the individual properties is an important task in visual basic. Note : If the property window is hidden for some reason, you can make it visible by pressing f4, clicking on the properties tool, or simply choosing view b property.
3.7 FORM LAYOUT WINDOW
46 The form layout window enables to preview the final location on the screen where the form one is working with will appear. If an application is having multiple forms, using the form layout window to align them properly onscreen can be easier than setting their properties by hand.
Using this window user can position forms as you want them to appear on the screen when they are first displayed. To give a Form new initial location, just drag that form in the form layout window to that new location.
3.8 TOOLBOX
The toolbox contains the various controls that can be placed on a form when mouse cursor is placed over any of the controls on the toolbar, a pop-up tool tip will appear, displaying a short description of the control.
When a new project is started, these controls are already added to the toolbox. However many more controls come with Visual basic 6 and they can be added to the toolbox whenever required. The method of adding these controls to the toolbox by using component option exist in project menu.
The user can use the toolbox to add controls to your projects, and you do so in a very easy way – by click a tool, such as the command button , and so on in the form. The toolbox is loaded with controls, user can add to form like text boxes, labels, picture box, Image box, labels, option button, check box, list box, timers progress bar, status bar, menu editor and more tools can be added in to the form.
47 3.9 The form designers and Code window
The last parts of the IDE that we have an overview are form designers and code windows, appears in above. The form designer displays the current form under design, complete with command button, and the code window displays the code for the Form_Load() procedure.
Form designers are really just windows in which a particular form appears. You can place controls into a form simply by drawing them after clicking the corresponding control s tool in the toolbox.
Code windows are similarly easy to understand: you just place the code you want to attach to an object in the code window to open an objects code in the code window, just double- click that object. There is two drop-down list boxes at the top of the code window: the left list lets you select the object to add code to, and the right list lets you select the procedure to add all the methods the object supports appear in this list.
48 3.10 HELP IN VISUAL BASIC
Using the Online help facilities
The online documentation included with Visual basic 6 actually contains answers to almost any question that the user will have while working in visual basic.
Micro soft has changed the format of online help files to match the new MSDN Library network. One can access the Visual basic Help system from the Help menu by selecting Contents, Index, or Search to access MSDN online. MSDN stands for Microsoft Developer Network, which includes MSDN CD-Rom subscriptions, an MSDN website, technical articles, and newsletters. Selecting Help b Contents will display the screen for complete help for users, when MSDN have separately installed in the system.
The available tabs offer the following options.
Contents - Enables to scan help contents organized in “books” by topic. Index - Enables to scan for help through indexed keywords. Search - Enables to perform a full text search of the information in the library. Favorites - Enables to store links to frequently used topics for easy retrieval.
Interactive help features
Most traditional help systems wait for the user to start eh interface and require information on a particular topic or question. Visual basic includes two very useful help – related features that no longer wait for the user. The two types of help are Auto List members Auto Quick Info
Auto list members are a time saving option that displays a list box which contains the members (properties and methods) that are available in the code window.
49
From the above example is that, while writing coding for command button1 in code window it displays the auto list member related to that command button. If the user type the term command1 the dot it displays the auto list members and then select the option which is required for the user by selecting simply or pointing it and the press spacebar.
By using the help of the auto list member concept that helps the user in time saving in typing the commands completely.
Note: If the control is placed or present in the current form, then while writing coding time if the user types command and press dot means the complier does not displays the auto list members because it displays only the control exist in the current form.
Auto Quick info option displays the syntax of any function, subroutine, or method. When the user one enters the name of that procedure followed by a period, space, or opening parenthesis. The procedure can be either a built – in – function or subroutine that is contained in visual basic or it can be one that is written by the user.
From the above dialog box is that the user is typing a coding for message box in code window for form _load event. At the time the general syntax of message box is displays while typing. From this information or help the user can able to continue the writing of coding to complete the whole statement without any help line from the other users.
50 LESSON-4 METHODS AND EVENTS
4.1 Methods and events 4.1.1 The Event procedure 4.1.2 Event Triggering 4.1.3 Mouse Events 4.1.4 Keyboard Events 4.1.5 Other Events 4.2 Event driven programming 4.3 Working with forms 4.4 Variables 4.4.1 Dimensioning of variables 4.4.2 Option Explicit statement 4.4.3 Variable assignment statement. 4.4.4 Modifying a Variable 4.5 Scope of variables 4.6 Constants 4.7 Data types
4.1 METHODS AND EVENTS
Events are responsible for everything that’s happening within windows. Events are an integral part of the widow operating system. Visual basic events help to create complex applications easily.
Pressing the keys, moving the mouse, clicking an object, and so on are the some of the events that happen in visual basic. The program understands the recent event that occurred and the responds accordingly.
If the user clicks the mouse in the application window, visual basic notices it and then sends a message to that application indicating that the event has occurred along with some additional information, known as parameters of the event.
4.1.1 The Event procedure
Knowing when an event occurs is the first step in using them in the application. When the user types something on the keyboard or uses the mouse, Visual basic will receive the
51 input from the event and then passes it on to the application. The application then decides how to react to that event.
An event can be ignored simply by not adding any code to its event procedure. Every object in the application has one or more events associated with following figures are that code editor with the drop down event list for the form.
If a new project is created and executed without adding any code, nothing would happen if any event is performed on the form. However, even if a single line of code is added to the form load event procedure for instance, it would be executed when the form is loaded.
4.1.2 Event Triggering
In a Visual basic application, two different types of events can occur. The first type is a user event; that is, something that the user does that triggers the event. The second type is a system event, or the user does not control something that occurs within the application. The system events include
Timer actions Data access errors From status changes Control status changes
As it can be seen, triggering an event controls all the actions in the program. Because of this, there are usually many ways for the user to trigger the same event. For example, the click event can be triggered in response to several other events besides just left – clicking the mouse on an object. The following are some of the other ways to triggers a click event.
52 Clicking the right mouse button on certain controls. Pressing the Space bar if a command button has the focus Pressing the Enter key if the command buttons default property is true Pressing the Esc key if the command buttons default property is true Pressing the hot key if it has been defined in the caption property.
From the preceding short list, it can be seen that there are a variety of ways to trigger a click event. This gives the control needed to complete a Visual basic application.
4.1.3 Mouse Events Many events can be triggered using the mouse. Each of them enables to response to them as needed. The mouse – oriented events are as follows.
Click - Occurs when a user presses the left mouse button Dbclick - Occurs when the user presses the left mouse button twice. DragDrop - Occurs when the mouse button is held down and dragged to another control that has Drag drop enabled. Visual basic responds by executing the Drag drop procedure for the target object. Drag Over - Occurs when the user is in the process of dragging an object. Mouse Down - Occurs when a mouse button is pressed. Mouse Up - Occurs when a mouse button is released. Mouse Move - Occurs when the mouse is moved over an object with no button pressed.
The following new project is used to explain the usage of these events. In the project a command button and the text box are first placed on the form.
53 Again without the code, this program will do nothing. The following code added to display a message in the text box when the mouse is moved over it and to displays message if the mouse is moved over the command button. If the mouse is anywhere else on the form both the message will be cleared.
Private sub form_mousemove (button as integer, shift as integer, x as single, y as single) Text1.text = “ “ End sub
Private sub command_mousemove (button as integer, shift as integer, x as single, y as single) Text1.text = “This is a sample program” End sub
Private sub text_mousemove (button as integer, shift as integer, x as single, y as single) Text1.text =”” You are learning Visual basic” End sub
4.1.4 Keyboard Events
Keyboard events enable the program to monitor any keyboard input that is passed to a program, and to validate and modify that input if needed. The main purpose of these events is input validation. The following three main events are associated with the keyboard.
Key press - occurs when a key is pressed but before the program actually processes it. Key down - occurs when a key is pressed. Key Up - Occurs when a key is released.
These events give the control needed to verify input in a professional manner. If a user presses a letter key when a numeric key is expected, the program should display an error message and the user to correct the error.
4.1.5 Other Events
Many other events can be used in the application that would be useful to perform certain actions when something starts or changes. Visual basic has been written to trap several states – change events so that the program will have a chance to respond if needed. The following are some of the events in this group.
Activate - Occurs when a form becomes the active window. Forms are activated using the show method.
54 Deactivate - Occurs when a form is no longer the active window. This can be done using Hide method. Got Focus - Occurs when an object receives the focus either by user action such as tabbing to or clicking the object, or by changing the focus in code using the Setfocus method. Lost Focus - Occurs when the focus is moved to another control either by user action, such as tabbing to or clicking another object, or by changing the focus in code using the Setfocus method.
Load - Occurs the first time a form a loaded. For a startup form this event occurs when an application starts as the result of a load statement or as the result of a reference to an unloaded form’s properties or controls. Unload - Occurs when the form is unloaded. This event is triggered by user closing the form using the close command on the control menu or an unload statement. Bu using these and many more status events, one can change the application with a great deal of control and enhanced appearance.
4.2 EVENT DRIVEN PROGRAMMING
Forms and controls are the basic elements in the user interface of any Visual basic application. In visual basic, these are called objects, because they are used like real world objects. Like any other physical objects, they also have properties and react to external events.
Consider that the fountain pen, for instance is a physical object and one of its properties is the colour of the ink used in the pen. When a pen is purchased the colour of the ink to be used in the pen is decided and that colour ink is used to fill up the pen. At the same time, at a later stage, different colour ink can also be used. Similarly most control properties of the visual basic objects are set when they are created and placed on the form. But the properties of those controls can be changed later by assigning a new value to it. This means that the properties of the visual basic objects can be assigned at design time through the properties window or at runtime though the visual basic program code.
4.3 WORKING WITH FORMS
The initial from window displays at the center of the IDE window. In that window by adding controls and changing its size can be customizing by the user. The size of the form can be controlled either by manually changing the height and width properties at design time and runtime or by selecting the form and dragging the sizing handles at design time.
55 The height property represents the form’s vertical size on the screen, whereas the width property represents the form’s horizontal size of the screen. To change the height and width properties at runtime. The form_ activate event is executed whenever the login form is initialized or get focus.
Private sub form_activate () Frmlogin.height = 2500 Frmlogin.width = 5000 Endsub
When F5 button is pressed to run the application, it can be noticed that the login form would have a changed its height and width.
The keyword Me can be used to refer to the currently loaded form object instead of explicitly giving the form name.
Private sub form _activate ( ) Me.height = 2500 Me.width = 5000 End sub
In addition to controlling the form’s height and width, one also can have control over its position on the screen during runtime. The relative position of the form can be controlled during design time by manually changing the Top and Left properties in the properties dialog box or by selecting the form and dragging the sizing handles at design time. The top property represents the distance from top edge of the object to the top of its container.
56 Again changes can be made at design time by using the properties dialog box. To change the top and left properties at design time, simply the desired property value selected and the new value is types. When the application is rum, the new property values will be used.
To make changes at runtime, some code segments need to be added to the application. Typically these code segments are not more than a few lines in length, but they give programmatic control over how the form or control is positioned during runtime. The coding will adjust the top and left properties so that the form is positioned in the upper – left corner of the screen.
Private Sub_form load ( ) Frmlogin.Top = 1000 Frmlogin.Left = 1000 End sub
The following are the common properties for Form
Caption - The caption property sets the title of the form. Name - This property is used only in code. Appearance - Determines whether the form will have three dimensional look. The default property value is 1. Border style - It consists of 5 values. The default value is 2, allows the user to size and shape the form. 1- Fixed single, 2- Sizable, 3- Fixed double , 4- fixed tool window, 5- sizable tool window. Control box - Changes to this property go into effect only when the user runs the application. Enabled - It has two status of true or false. If it false that the form will not responded to any event occurred. Font - It can use to change the font used to display information on the form. Height, Width - This property will affect the form height and width while in design time itself. Icon - This property determines the icon your application will display when it is minimized on the toolbar or turned into a stand – alone application on the windows desktop.
57 Visible - This has a value of true and false. If you want to make form invisible only when you are designing an application with multiple forms. Window state - This property determines how the form will look at run tie. A setting of 1 reduces to icon; setting of 2 maximizes the form, setting 0 to the normal default setting.
4.4 VARIABLES
Computer program have the capability to work with and store information to be used in many different processes. This requires that the program can store and manipulate that information whenever it is needed. This is done using variables.
A variable is a location in memory that is given a name. The name given to a variable may be almost anything, although there are some restrictions. A variable can be declared simply by using a name in the program.
Example: A Memory location for data storage.
A = 100, here a is memory location with variable name is A.
However, if option explicit is specified in the general declaration, every variable must be defined or an error will occur.
Variables in Visual basic hold information (values). Whenever you use a variable, visual basic sets up an area in the computer memory to store information. Variable names in visual basic can be up to 255 characters long and provided the first character is a letter, can include any combination of letters, numerals, and underscores.
The rules for declaring a variable in visual basic 1. The name must begin with a letter (a to z , A to Z). 2. The name can contain only letters, numbers, or the underscore character. 3. It must not exceed 255 characters. 4. It cannot be a Visual basic reserved word. However, it can contain a reserved word like opencustomer is valid one, but open is invalid one.
It is better to declare any variables in the program explicitly using a DIM statement as shown below. Dim str as string Str = “Best of luck”
58 4.4.1 Dimensioning of variables
I order to declare or dimension a variable in the program, the DIM statement is used. This informs the computer that the user wants to declare a variable. It also specifies the name and the data type of the new variable.
The following is the syntax of the DIM statement.
Dim variable_name [as variable _type]
The variable_name is the name to be used for that variable. The as variable_type is an optional parameter.
The following example shows a routine in visual basic using DIM statement.
Private sub form _ load () Dim frm as Boolean Dim msg as string Frm = true Msg = “welcome to India” Print” This is demo “, msg End sub This code declares both variables prior to actually using them. By using this method, the amount of space that the program uses when executing is reduced. Another benefit of declaring variables this way is that visual basic will displays any type mismatch error that might occur.
Output This is demo welcome to India
4.4.2 Option Explicit statement
When dimensioning variables, there is one pitfall that must be watched out. If a variable is not explicitly declared in the program, visual basic will implicitly declare it and the application developer will never realize it. The same thing will happen if a variable is misspelled; however, the program might not work correctly because there is now an extra variable being used. To prevent this from happening, the option explicit statement should be used in the declaration section of each form as shown in the following figures.
59 The option explicit statement will instruct visual basic to display an error for any variables that was not explicitly dimensioned in the program. To ensure that this setting is always turned on, the option in visual basic can be set so that every form or module that is added to a project will automatically have this option added to it. This can be done by selecting Tools b options from the visual basic menu to display the options dialog box as shown below.
By clicking the Require variable declaration setting, the option explicit statement will be included in every new form or module that is added to a project.
60 4.4.3 Variable assignment statement Assignment statements are what you use to give a visual basic variable a new value. Another way is to think about assignment statements as a means of copying information from the source to destination. In any case giving values to variables is one of the most common tasks in visual basic code. Visual basic uses an equal sign for this operation
For example
Test = 100
Here it set the value of a variable named test = 100. The variable name always appears on the left of the equality sign, and the value always appears on the right. Visual basic must be able to obtain a value from the right side of an assignment statement, and it will do any processing needed to make this happen. For example Test1 = 25 + 5
Here it would make the variable test2 have value is 30. This is because Visual basic would do the addition first, and then store the result in the variable.
4.4.4 Modifying a Variable
Constants are variables that cannot be modified within the program while it is executing. A constant, as the name implies, cannot be changed. If a value is needed in several different sections of code, it is recommended that this value is declared as a constant.
There are two main benefits of using a constant in the program. First one need not have to remember a specific number to type into every section of code that uses it. A constant can be declared to be equal to that number and that constant can be used wherever that number is referenced. The second benefits is the ability to change one value in the declaration section of the program, and have all the references to it change automatically. The syntax of a constant declaration is as follows
Const variable_name [as variable type] = value
Declaring a constant is similar to declaring a variable except for the assignment portion of the statement at the end of the declaration.
4.5 SCOPE OF VARIABLES
Project Scope
An objects scope indicates how much visibility it has throughout the project in the procedure where it s declared, throughout a form or module, or global scope ie. Which means it’s accessible everywhere. There are two types of scope in Visual Basic projects: variable scope (including object variables) and procedure scope.
61 Variable Scope
The user will use the Dim statement to declare a variable. If you do not specify the variable type when you use Dim, it creates a variant, which can operate as any variable type. You can specify the variable type using the as keyword like this:
Dim ab As Integer
Besides Dim, you can also use ReDim to redimension space for dynamic arrays, Private to restrict it to a module or form, Public to make it global that is, accessible to all modules or forms or Static to make sure its value doesn’t change between procedure calls. These ways of declaring variables are summarized in
Visual Basic declaring statements.
Keyword Meaning Dim Using Dim alone creates variants. Use the as keyword to specify variable type. Private Makes variable available only in the current form/module. Public Makes variable global variable is available to the rest of program. ReDim Reallocates storage space for dynamic array variables. Static Variable preserves its value between procedure calls. Type Declares a user type.
There are three levels of variable scope in Visual Basic: at the procedure level, at the form or module level, and at the global level.
Procedure Scope
As with variables, you can restrict the scope of procedures, and you do that with the Private, Public, Friend, and Static keywords. The Private and Public keywords are the main keywords here; using them, you can specify if a subroutine or function is private to the module or form in which it is declared or public (that is, global) to all forms and modules. You use these keywords before the Sub or Function
Example Private Function ret() Dim test test = 7 ret = test End Function
62 In visual basic user can also declare procedures as friend procedures with the Friend keyword. Friend procedures are usually used in class modules (they are not available in standard modules, although you can declare them in forms) to declare that the procedure is available outside the class, but not outside the current project. This restricts those functions from being called if the current project serves as an OLE automation server.
Thus the earlier declarations, you can also declare procedures as Static, which means that the variables in the procedure do not change between procedure calls, and that can be very useful in cases like this, where we support a counter variable that is incremented each time a function is called:
Static Function Count () Dim CtVal as Integer CtVal = CtVal + 1 Ct = CtVal End Sub
The following is the systematic of visual basic project scope.
Global Items Declared with PUBLIC
Form
Form – Level variables Declared in General
Private variables Available to this form only
Procedure Procedure Local Local Variables Variables
63 Global Items Procedure Procedure Declared with PUBLIC Local Local Variables Variables
Module
Module – Level variables Declared in General
Private variables Available to this module only
The scope of a variable refers to how long it can be used and which routines can see it. There are three different types of scope a variable can have Global, Module, and Local.
1. Local Scope
Whenever a variable is declared inside a function, subroutine, or event routine, only the code within that procedure can see that variable. This is referred to as local scope. The following two routines with local variables defined in them.
Example
Sub routine1 ( ) Dim var1 as Integer Dim var2 as String Var1 = 5 Var2 = “Sample program” End sub
64 Sub routine2 ( ) Dim var1 as String Dim var2 as Integer Var1= “Sample program” Var2 = 15 End sub
As it can be seen, the same variable names can be used in separate routines because they are local to each routine and are not known by the other routine.
2. Module Scope
The next type of scope is called module. A variable can be declared with module scope by using the private declaration statement. The syntax of the private statement is the same as a Dim statement except for the keyword private. Any variable declared as private can be seen in any routine within the module or form where it was declared. The following is the same as the preceding example except it uses the tern private to define the variables.
Example
Private var1 as Integer Private var2 as String
Sub routine 1() Var1 = 10 Var2 = “welcome to India” End sub
Sub routine 2() Var2 = “welcome to India” Var1 = 10 End sub
As seen in the above example, once the variables are declared outside the routine, the same variables name cannot be used for different data types.
3. Global Scope
The last and most powerful of the scope is global scope. To define a variable as global, the public declaration statement is used. The syntax of the public statement is the same as a Dim statement except for the keyword as Public. Any variable defined as public can be used by any routine in any module, within the program.
The following declaration shows that the variables used in the preceding example. After this is done, they can be used in any routine as shown in the later part of the coding.
65 Example
Sub routine1 () Var1 = 15 Var2 = “welcome to India” End sub Sub routine2 () Var2 = “welcome to India” Var1 = 15 End sub
4.6 CONSTANTS
Declaring Constants The term constants are nothing but the value cannot be changed during the execution of a program for particular time period. Declare them all in one place, and then refer to the constants by name throughout the code instead of hardwiring numeric values in the code. When its time to change those values, you just change the constants, all in one well- defined part of the code. The user can declare constants in Visual Basic with the Const statement: The general format is
66 [Public | Private] Const constname [As type] = expression The Public keyword is used at the module level to make a constant global. This keyword is not allowed in procedures. The Private keyword is used at the module or form level to declare constants that are private, which means only available within the module or form where the declaration is made. Like the Public keyword, Private is not allowed in procedures (constants in procedures are always private anyway). The constname identifier is the actual name of the constant. The type identifier is the data type of the constant, which may be Byte, Boolean, Integer, Long, Currency, Single, Double, Date, String, or Variant. The expression identifier holds the value you want for this constant. It may be a literal, other constant, or any combination that includes all arithmetic or logical operators (except the Is operator). You can use a constant anywhere you can use any Visual Basic expression, and you usually use them for numeric or string values that you want to use many places in a program. That way, when you want to modify the value of the constant, you only have to change it in its declaration, not in many places around the program. Also, constants don t change their values, which can make them more useful than variables in certain circumstances.
Here is an example showing how to declare and use a constant:
Private Sub Command1_Click ()
Const Pi = 3.14159
Dim Radius, Area
Radius = 15
Area = Pi * Radius * Radius
Print ("Area = " & Str (Area))
End Sub
Note:
From the above program is that the value of pi is assigned in global as a constant for particular period of time. When the statement executes the value of pi is assigned as 3.145 and then it do calculations for further steps. The term constant is nothing but value cannot be changed for particular time duration.
67 4.7 DATA TYPES
The different data types available in visual basic represent the types of data that visual basic uses are given below in the table.
Any of these different data types can be declared as a variable. The default storage types for a variable are Variant. If the data type is not specified, then variant will be used for processing.
Data type Description Declaration Character Range Byte 1 byte None 0 to 255 Boolean 2 bytes None True or False Integer 2 byte integer % -32 768 to 32,768 Long 4 byte integer & 2,147,483,648 to -2,147,483,648 Single 4 byte floating ! 3.402823E38 to point number -3.402823E38 Double 8 byte floating # 1.79769313486232D308 to point number -1.79769313486232D308 Currency 8 byte number @ 922,337,203,685,477,5808 to with fixed decimal -922,337,203,685,477,5808 Object 4 bytes None Any object reference Date 8 bytes None 1/1/100 to 12/31/9999 String String of characters $ Through characters 65,500 Variant Date / Time None Can contain numeric data in Floating point the range as a double, or any Numbers or strings string character.
Note:
Variant is the most flexible type of variable that can be used. It can be used to work with most of the other data types, except for fixed – length strings. However, there are some problems with using that variant data type. For example, one could have two variant variables, one that is a string and the other that is number. Visual basic does not allow the arithmetic operations of these two variables together because they are different data types.
1. String The string data type holds characters. User can have a single character in a string or many. A variable holding a string is called, naturally enough, a string variable. One method of identifying variables of this type is to place a dollar sign ($) at the end of the variable name
68 Example
Stringvariable$. Once users add the dollar sign, that variable can only hold strings. String variable can theoretically hold about 2 billion characters. On a specific computer, though the variable may hold less, due to memory constraints. One of the most common uses of string variables is to pick up the information contained in a text box. For example if user has text box named as test1, then
Test1$ = text1.text.
Here it assigns the string contained in the text box to the variable named as test1 on the left hand side of the assignment.
2. Integer Integer variables hold relatively small integer values (between -32,768 to 32, 768). Integer arithmetic is very fast but is restricted to these ranges. One way to make sure that a variable will only be capable of holding integers is to use the percent sign (%) at the end of the variable name.
Example Test% = 5
3. Long Integer
The long integer variable holds integers between 2,147,483,648 to -2,147,483,647. The identifier can use for your variables is the ampersand (&). Long integer arithmetic is also fast, and there is very little performance on modern machine.
Example Test& = 123456789
4. Single Precision
The least accurate is called single precision. They have a decimal point, but user can be sure of the accuracy of only seven digits. The accuracy is limited; the size (range) of these numbers is up to 38 digits. For single precision numbers, the identifier user can use to make sure a variable will only hold a single precision number is an exclamation point (!). Example Test! = 12.456
4. Double Precision
The double precision data type is used when user need numbers with up to 16 places of accuracy; they will also allow user can have ore than 300 digits. Double precision
69 variables are mainly used in scientific calculations in visual basic. The identifier used for double precision variables is a pound sign (#). The user has to use the Pound # symbol at the end actual number.
Example Test# = 12.5435000000000
5. Currency
Currency variables are type that will be new to programmers. They are designed to avoid certain problems inherent in switching from binary fractions to decimal fractions. The currency type can have 4 digits to the right of the decimal place and up to 15 to the left of the decimal point. Arithmetic will be exact within this range. The identifier is an “at” sign (@).
Example Test @ = 12.45668
6. Date The date data type gives you a convenient way to store both the date and time information for any time between midnight on January 1, 100 to midnight on December 31, 9999.
Example
Test = # January 1, 2008# Test = # Jan 1, 2008# Test = # 1 / 1 / 2008#
7. Byte
The byte data type can hold integers between 0 to 255. This is a great convenience when you need to save space, and it makes certain arrays much smaller than they would have been in earlier version of VB.
8. Boolean
The Boolean type when user needs data to be either true or false. It is considered good programming practice to use this data type rather than integers for true or false values.
9. Variant
The variant data type is designed to store all the different possible VB data received in one place. It does not matter whether the information is numeric, date / time, or string; the variant type can hold it all.
70 UNIT – III
Lesson – 5 5.1 Functions 5.1.1 Writing a simple functions 5.1.2 User defined function with example 5.2 Procedures
Lesson - 6 6.1 Define control Structures 6.2 If concepts 6.2.1 IF..THEN ..Else 6.2.2 IF..THEN…ElseIf 6.3 Switch – Select 6.4 For looping 6.4.1 For…Next statement 6.4.2 Step statement 6.4.3 Exit For statement 6.4.4 Nested For…Next 6.5 While looping 6.5.1 Do – While loop 6.5.2 Do – Until loop Lesson – 7 7.1 Arrays 7.2 User defined data types 7.3 Data type conversions Lesson – 8 8.1 Operators 8.2 String functions 8.2.1 String handling functions 8.3 Date and time functions
71 LESSON-5 FUNCTIONS
5.1 FUNCTIONS
5.1.1 Writing a simple function
5.2 PROCEDURES
There are actually two kinds of general procedures in visual basic:
Function procedures and Sub procedures.
Function procedures or user defined functions are simply ways of going beyond the built in visual basic functions. Sub procedures on other hand are smaller helper program that are used as needed. Sub procedures are thus generalizations of the event procedures. The point is that sub and function procedures do one or more of the following
Help you break down large tasks into smaller ones. Automate repeated operations Make it clearer what it is you are trying to accomplish by “naming” a piece of code. All these features can dramatically reduce debugging time.
5.2.1 Writing a simple function
Before writing the user defined function the user has to make some settings in the visual basic. First click Tools menu b Add procedure, and then user will get the Add procedure dialog box like as follows. In that dialog box consist of following options for further processing
1. Name 2. Type - Sub , Function, Property, Event 3. Scope - Public , Private 4. Ok button 5. Cancel button
72 From the above dialog box user have to type the name of the function. And also select the type as sub, property, function, events. After that user has to select the scope of the function may be public or it may be private. Finally has to click te ok button in the dialog box. Then the user will get the following type of window for writing coding for processing the user function.
The following is the general format for writing user defined functions as a separate block in your coding area.
Public / private function function_name (parameters) Statement or block of statements End function
73
Example
Public function random(x) as integer Random = int(x * rand) + 1 End function The output of the above is that the value of x is assign as random values form the memory and it’s incremented by one, for time of execution of the grouping statement.
Note: The first line of the function (line containing the name) is called as the header of the function. The keywords public or private are called as access specifier. Here the variable X is called as formal parameters.
While naming the function name the user must following some condition or rules would be same as the variables name rules.
Example Public function random( X ) Public function random( X ) as integer In both the cases visual basic will the know that function returns integer values.
Body of the function
Random = int ( x * rnd ) + 1
Note: Next come to the body of the function – code that actually defines the functions power. This assignment statement is how the function gets its value, then it depends on the x that occurs both here and in the header of the function. Here the variable called actual parameters and it also called as place holders.
The following are concept of parameters used in different types in functional statement. 1. Public function random (X) as integer 2. Public function random (X as integer) as integer
From the above two types of defining function statements, in that first one the parameter is a variant because we have not used any type identifier. If user want to ensure that only integers to the function we should like a statement two.
Example a = 2 , b= 10 and the function statement followed by r= random ( a * b + 5)
74 this will effect same as the following type by r= random (25) Here in the above two type of functional statement is that process is the same, but in first statement the expressions is passing as a parameter. In second statement, instead of parameters the constant value is passing directly for further processing. Function with more than one parameter
Example The following is a function concept consists of more than one parameter or two parameter. Public function test(x as integer, y as double) Functional statements End function
Note:
1. Here the function name is test 2. The function is declared as public access specifier 3. It consist of two variables or parameter like a and y 4. Then used defined programming statements. 5. Finally the function ends with end function keyword.
5.2.2 Further more on User defined function with example
The following is the simple form of defining the user defined function is as follows Public function fun_name( parameter1, parameter2) Statements Function name= expression1 Function name = expression2 Statements End function
Here parameter1 and parameter2 are referred to as the arguments or variables in the function. Then the expression1 and 2 is assigned to its corresponding variables or function name for further processing. Example
In code window Dim A as integer Pubic sub command_click ()
75 A = val( text1. text)
Test (A) // This is calling statement
End sub
Public function Test(x as integer) // the X gets the value of A
Test = x + 10 // here it calculate the value of x and 10
Print “the result is “, test // finally it print the result value
End function // end of the function
Example
In code window
Dim A, B as integer
Pubic sub command_click ()
A = val( text1. text) B = 10 Test (A, B) // this is calling statement for function with two parameters
End sub
Public function Test(x as integer, y as integer) // the X gets value of A and Y gets B r= test( x + 10) // here it calculate the value of x and 10 m = test(y * 5) // calculate the value for m
Print “the result for R “, r // finally it print the result value for r
Print “the result for M”, m // it print the value of M
End function // end of the function
Output:
76 Consider the value of A is given in text box is 15 and value of B is already assigned the value as 10. So the value of A and b is assigned to the variable X and y by calling a function called test. In test function the value of X is added with 10 and its value is assigned to the variable R and also the value of Y is multiplied by 5 and assigned in variable the M. Finally the value of R and M is printed using print statement. The result of R is 25 and the result of M is 50
5.2 SUB PROCEDURES
To define the sub procedure execute as same way as the function click on tool menu b add procedure. The following is the general format for sub procedure concept.
Public sub nameof_sub (parameters) Statements End sub
Note: First line of the above block is that called as header of the sub procedure. Along with that the access specifier is mentioned in that statement. The private or public keyword s used. In header section the name of the sub procedure is highlighted. Then followed by statements for processing and finally end with the end sub.
Pubic sub comman_click() a = val(text1.text) call test( a) // calling statement for sub procedure end sub // end of the main block
public sub test ( x as integer ) // x receives the value of a. res= test(x + 10) // calculate the value of res print “the result evaluate in sub procedure “, res //print the result end sub // end of sub procedure
77 The following are the type to call the sub procedures 1. name of procedure( argument1, argument2) 2. call name of procedure ( argument1, argument2)
Example
Public Sub form_click()
Dim a as integer
For x = 1 to 5
Call test ( x ) // call for sub program,
Next X Print “ The result in block main” End sub
Sub test ( x as integer) // sub program starts executes here.
Print “result in outer loop or sub program”, x
End sub
Output
From the above program is that while at the time of form load event will execute and the first time for loop starts executes it first execution and its assign the value of X is 1 and its calls the sub procedures called test. In sub procedure the using print statement print as “result in outer loop or sub program “with value of x.
“Result in outer loop or sub program “ 1 “Result in outer loop or sub program “ 2 “Result in outer loop or sub program “ 3 “Result in outer loop or sub program “ 4 “Result in main block”
Advanced concept of function and sub procedure
The advanced concept of function and sub procedure consists of following concept
When user calls a function or procedure, there are actually tow ways to pass in variables as arguments. These are called
Passing by reference Passing by value
78
When you pass argument variables by reference, any changes to the corresponding parameter inside the procedure will change the value of the original argument when the procedure finishes. When you pass an argument by value, then original variables retains its original value after the procedure terminates – regardless of what was done to the corresponding parameter inside the procedure.
Example
Sub form_load()
Dim A as integer
A = Val (text1.text) // consider A = 5 Print “value of A in main block “, A
Test (A)
End sub
Sub test ( x as integer)
R = test ( x + 25 )
Print “ result in sub block “, R
End sub
Output A is assigned a value as 5 Then it prints as in same block using print statement. Again the value of A is passing to the sub program and its value is incremented by 25.
“Value of A in main block “ 5 “Result in sub block “ 30
Note: When the program starts running and visual basic executes the above statements the variable named A is passed by reference to the parameter X.
A = 5 Here the value a = 5 is assigned first
79 Here the value of x = 5 is referred the variable A X = 5
Example
Dim a, b as integer
a = 5 b =15 print test ( a, b) // call sub program print “ the value of A is “, a print “ the value of B is “, b
end sub
Sub block
Public function test( x as integer , y as integer)
Res = test( x + y + 15) // calculation of a and b
Print “the result after addition of two values A and B”, res
End sub
Note:
From the above program is that value of a = 5 and b = 15 is assigned first then its value is passed to the variable called x and y. Through this value of x and y the result is evaluated. Finally the result value is displayed as output.
Output The value of A is 5 The value of B is 15 The result after addition of two values A and B 35
80 LESSON-6 DEFINE CONTROL STRUCTURES
6.1 Define control Structures 6.2 If concepts 6.2.1 IF..THEN ..Else 6.2.2 IF..THEN…ElseIf 6.3 Switch – Select 6.4 For looping 6.4.1 For…Next statement 6.4.2 Step statement 6.4.3 Exit For statement 6.4.4 Nested For…Next 6.5 While looping 6.5.1 Do – While loop 6.5.2 Do – Until loop
6.1 DEFINE CONTROL STRUCTURES
When designing a new application, the developer needs to control the different sections of code that would be executed depending upon the data being processed. This process is commonly referred to as conditionally executing the program code.
In order to execute certain sections of code conditionally the program, should respond to a condition or test. If the condition is true, then the code will processed. This process is the basis of every program that is written.
Thus in visual basic looping or control structures divides into two types are 1. Determinate loop 2. Indeterminate loop
In Determinate loop the following concept are included 1. For.. Next 2. Nested For..Next
81 For Indeterminate loop consists of 1. do …While loop 2. do. ..Until loop
Among this the If..then else concept is different from other type of loping concept. Because the If..then concept will execute it for specified conditions. Based on the conditions the control will transfer the flow in programming statements.
If consist of two type 1. IF..then …else 2. IF.. then … Elseif ..endif 3. Nested IF..then concept
6.2 IF CONCEPTS
Although there are many different ways to perform this test process, there is one primary way of doing it. The visual basic statement for performing these tasks is the If…then…….End if Statements.
Before going to the If…then … else concept, in visual basic we have a simple if…then concept without else part section.
The general format is
IF (condition) then do action for true statements
Other wise it execute the next statement in program
Example
If ( a > 10 ) then print “ A is greater than 10” Endif Next statements in programming block
Note: From the above example is that it checks for condition that value of A is compared with 10, i.e value A is greater than 10 then it executes the true part of then part section. If it is the conditions is set to failure of condition then it execute the next statement belongs to the programming statements.
82 Example
IF( a = b) then Msgbox (“A value is equivalent to value B”) End if Next statements belongs to the programming block
Note: From the above example is that the value of A is compared or checks for equivalent value of B, then it is true means then it execute the statements called true part will be executed. It gives the result in message box as a message. Other possible out come is that the condition is false the control is transfer to the outside of the loop and it execute the statement belongs to the programming statements.
6.2.1 IF..THEN ..Else
Even though IF statement is very powerful, it can test only one condition at a time. If is required to test more than one condition at a time, there is a way to use the If statement to check multiple conditions. This can be done adding the Else and Else IF statement for further processing in the programming blocks.
The following is the general forma t for IF..then Else statement.
IF (Condition) then True block statements Else False block statements
Example
Visual basic to check greatest of two numbers between A and B
A = val ( text1.text) B = val (text2.text)
If (A > B) then Msgbox ( “The Greatest number is A “, A) Else Msgbox ( “The Greatest number is B “, B) End if
83 Note:
From the above program the value of text box1 is assigned to the variable to the A and same as the value of text box2 is assigned to the variable to the B. Then the value of A and B check for greatest value among two numbers. First it checks that A > B then, if the condition is true then it executes the message box with the message of “The greatest number is A”. If the condition is false then it executes the statement regarding false section. It displays the message called “The greatest number is B”.
The key aspect while using If…then …else concept then its compulsory to that close the concept with End if keyword.
Example The program to check for two conditions in same statement
A = val ( text1.text) B =val (text2.text) C =val (text3.text) If ( A > B and A > C ) then Label1.caption = “A is greater among three numbers” Else Label1.caption = “The A is not a greater value among three numbers” End if
Note:
From the above program is that the value of text box 1, 2 and 3 is assigned to the corresponding variables like a, b and c. Then using if then else concept user is checking that two conditions at a same statement. If both the condition is true then it executes the true block statements. And it displays the output label1 in caption property. If the condition is false value then it displays that caption value of label1as A is not a greater value among three numbers.
Output Consider the following types of values to get the different output 1. A = 15 , B=10, C= 5 “A is greater among three numbers” Another combination of value 2. A = 5 , B=15 , C= 25 “The A is not a greater value among three numbers”
84 6.2.2 IF..THEN…Else If
The If…then concept is used to check for two conditions, but user want to check for more than two conditions then user can use the If…then Else if concept to reach the specific goal. At the end of the loop must end with key word called end if. Here only one block able to execute for processing based on the condition is satisfied.
The following is the general format for IF…then ….Else If
Syntax IF (Condition) then Statements Else if (conditoin2) then Statements Else if (condition 3) then Statements Else if (condition 4) then Statements Else Statements End if
Example
A = val (text1.text) If ( A = 5 ) then Msgbox “ A is equal to 5” Else if ( A = 10 ) then Msgbox “ A is equal to 10” Else if ( A = 20 ) then Msgbox “ A is equal to 20” Else if ( A = 25 ) then Msgbox “ A is equal to 25” Else Msgbox “ A is not equivalent to any groups of above” End if
Note: From the above program is that the value of text box1 is assigned to the variable A. First the value of input given by user is assigned variables A. Then the value of A is checks for condition is A= 5 , if the condition is true then it displays the message as “A is equal to 5” and exit the loop immediately. If the first condition is not satisfied then it checks for second condition in else if statement i.e. A = 10 then if it true then it displays a message as “A is equal to 10” and exit the loop.
85 Similarly the other condition also will be checked one by one and executes the corresponding statements. if non of the condition is satisfied then it finally control transfer to the else part that is false part in the loop. After the execution of false part it exits the loop.
Output Consider that value of text box is 5 then output is “A is equal to 5” is displayed in message box. Else the value of A = 10 then it displays a message “A is equal to 10” and so on. Finally no condition is matched then it displays the “A is not equivalent to any groups of above” in message box.
The following is the logical diagram for if…then...Else condition concept.
If Condition Checks
Statements in Statements in Else part True part
Example
X = val (text1.text) If ( X > 5 and X < 10 ) then Msgbox “The value range between 5 and 10” Else if ( X >10 and X < 20 ) then Msgbox “The value range between 10 and 20” Else if ( X > 20 and X < 30 ) then Msgbox “The value range between 20 and 30 “ Else Msgbox “The value is not belongs to any range data” End if Note: From the above program is that value of text box one is assigned to variable x. Then the value is checked for multiple conditions and based on that the statements will execute.
86 First it checks for x is greater than 5 and x is less than 10 then it displays the output in message box as “the value is rage between 5 and 10. By the same procedure it checks for other conditions. Once if the condition met a true then it execute the corresponding statement and exit the loop immediately. Through out the looping condition, no condition is matched then it automatically it executes the else part statements.
6.3 SWITCH – SELECT CASE
Another method that can be used to perform conditional processing is the select case statement. It is very useful when one must check a single variable or expression for ore than one value. The concept of If…then...else if concept is use for multiple conditions, from that one part will be executed. By using the if…then …else if concept leads the user to confusion and also the output is not exactly correct. To over come the problems in If concept, the select case concept will full fill the requirements of user needs. Using select case one can specify the expression that needs to be tested and than list all the possible cases or values that are to be responded with special action.
The following is the general format for Select…case concept
Select case (expression / variable) Case numbers / variable Statements for first case Case numbers / variable Statements for second case ------
Case else Statement for case else part. End select
Note: Here the select case starts with select case statement and it consists of variable or expression is passed as a arguments. Then based on the arguments the Case will execute and displays the output. Finally no cases is matched then the default or case else will be executed. If any case is matched means, it executed the case block statement and it comes out of the loop.
87 Example Visual basic program using Select case concept to display the variables component of computer name. X = val(tex1.text) Select case ( x ) Case 1: Print “The input value of x is one” Print “The one value is equivalent is motherboard” Case 2: Print “The input value of x is two” Print “The two value is equivalent is processor” Case 3: Print “The input value of x is three” Print “The three value is equivalent is RAM” Case 4: Print “The input value of x is four” Print “The four value is equivalent is Hard disk” Case 5: Print “The input value of x is five” Print “The five value is equivalent is ROM Case else Print “The input value of x is out of range” Print “Please enter the value between 1 and 5 “ End select
Note: From the above example is that input value is given in text box is assigned to variable X. Then the variable is passed to the function called Select case concept. If the input value is one then the select case function will match the first case and it displays the output. If it is two means it executes second case statement. If none of the cases is matched means that it executes / matched the case else part and it displays the output.
Output If user input is x = 1 “The input value of x is one” “The one value is equivalent is motherboard”
If user input is x = 2 “The input value of x is two” “The two value is equivalent is processor”
If user input is x = 3 “The input value of x is three” “The three value is equivalent is RAM”
88 If user input is x = 4 “The input value of x is four” “The four value is equivalent is Hard disk”
If user input is x = 5 “The input value of x is five” “The five value is equivalent is ROM
If user input is x = 6 or 7 or more “The input value of x is out of range” “Please enter the value between 1 and 5 “
Example Visual basic program using Select case concept to display the variables component of computer name.
Dim x as string X = Val (tex1.text) Select case ( x ) Case ‘M’ Print “The input value of x is M” Print “The one value is equivalent is motherboard” Case ‘P’ Print “The input value of x is P” Print “The two value is equivalent is processor” Case ‘R’ Print “The input value of x is R” Print “The three value is equivalent is RAM” Case ‘H’ Print “The input value of x is H” Print “The four value is equivalent is Hard disk” Case ‘O’ Print “The input value of x is O” Print “The five value is equivalent is ROM
Case else Print “The input value of x is out of range” Print “Please enter the character like M, H, O, R, and P “ End select
89 Note: The example consists of select case concept with character as an input for processing the block. Here the user is giving the input in the form of character type in text box. The input given in text box is assigned to the character variable x and it is passed to the function called select case.
If the user is giving input as X = ‘H ‘ then it execute the corresponding case statement and it displays the output as hard disk information. If input is R then it displays the output as RAM information. If the input is M then it displays the output as motherboard details. Like the way all other cases will executes. If none of the case is not matched for input value then the control is automatically executes the default / else case statement will process for output.
The important point while discussing the select case concept in character based input is that is case sensitive one. The capital letter has a different meaning compared to the lower case letters. So users have to consider the upper case and lower case letter while giving input.
Example
Consider that the user input value of x is ‘h’ in above example, then complier checks for all cases and it displays only the case else because the input value in lower case letter called ‘h’. But in the case statements we have only coded as “H”. So the complier will not match the corresponding statement.
Output If user input is ‘M’ “The input value of x is M” “The one value is equivalent is motherboard” If user input is ‘P’ “The input value of x is P” “The two value is equivalent is processor” If user input is ‘R’ “The input value of x is R” “The three value is equivalent is RAM” If user input is ‘H’ “The input value of x is H” “The four value is equivalent is Hard disk” If user input is ‘O’ “The input value of x is O” “The five value is equivalent is ROM If user input is other than M, P, R, H, O character means then “The input value of x is out of range” “Please enter the character like M, H, O, R, and P “
90 6.4 FOR LOOPING
6.4.1 For…Next statement
In an application much of the processing may be repetitive in nature. To perform these tasks, one would use one of the several forms of loop statements available in visual basic. A loop comprises of instructions that are executed repeatedly until some specific condition is satisfied.
This type of loop is called a counter – style loop process. It is done by incrementing a counter as part of the loop processing. The syntax of the For…next statement is as follows.
For counter = start to end [ step value ] Statements Next [ counter ]
Looking at the different parts of the FOR statement, one can see that the keyword FOR begins the loop process. The variable counter contains the current iteration of the loop during its execution. The start value represents the beginning value of the counter, and End specifies the number at which point the loop will terminate. The option al parameter step enables the specification of the value that is added to the counter after each iteration of the loop.
The final statement in the loop process is Next statement, which informs visual basic that it should increment the counter and return to the top of the loop. This statement also checks to see whether the counter value has reached or passed the End value specified, if it has the loop will not be repeated and execution to the next statement after the loop.
The following is the logical diagram for FOR…..NEXT concept in visual basic.
91 Set counter Variable to Starting value
If Counter YES Greater Value
NO
Body of Loop
Increment Counter Variable
Move to statements After the body Of loop
92 Example
For I = 1 to 5 // beginning of loop with step value as one
Print (“Welcome to FOR…NEXT Concept”) Print (“Statements inside the looping”)
Next I // increment the value of i by one
Note From the above example is that consist of For…Next concept. First it starts executes from I = 1 and it check the condition for less than 5, if the condition is true then it executed the body of the loop. Then after one time execution its counter variable “I” is increment by default one. Then again the value of i is check the came condition in for loop and continues the same till the condition becomes false.
Output Welcome to FOR…NEXT Concept Statements inside the looping Welcome to FOR…NEXT Concept Statements inside the looping Welcome to FOR…NEXT Concept Statements inside the looping Welcome to FOR…NEXT Concept Statements inside the looping
Example
For…next in default it checks condition in less than value and executes in sequential order. The same way another format of for…next statement executes in reverse order.
For I = 5 to 0
Print” Executes the loop in reverse order “ Print” The counter variable value decrease by one in default”
Next i
Note: From the above program is that the variable “I” value start execute from 5 and it checks for greater than condition, if it is true then it execute the statements in body of the loop. After the execution of one iteration then the counter variable “I” is automatically decrement value by -1. Then again it checks for condition and repeat the loop same, till the condition becomes false. The step value for reverse type of For…next concept is – 1 and also user can mention the step value by -2, - 3 etc.
93 Output Executes the loop in reverse order “ Print” The counter variable value decrease by one in default” Executes the loop in reverse order “ Print” The counter variable value decrease by one in default” Executes the loop in reverse order “ Print” The counter variable value decrease by one in default” Executes the loop in reverse order “ Print” The counter variable value decrease by one in default”
6.4.2 Step statement
The step statement of the For…next loop is optional one. However, it ca be useful depending on what a particular loop process is required to do. A step value need not be defined while writing a for loop.
The following two statements are identical because of eh default value of step parameter.
For I = 0 to 5 Both the statements are same action. For I = 0 to 5 step 1
The step statement enables to skip over certain numbers or elements in an array by changing the value by which the counter is incremented.
Sometimes there will be a need to start at the largest value and work backwards. This is also done using the step statements. by specifying a negative value for the step, the counter will be decreased by that value.
The step value plays an important role in for..next statement. Based on that value of step, the control or flow of the execution of loop will be changed.
Example For I = 10 to 0 step - 5 Print” Executes the loop in reverse order “ Print” The counter variable value decrease by user view of -5”
Next i Output Executes the loop in reverse order The counter variable value decrease by user view of -5 Executes the loop in reverse order The counter variable value decrease by user view of -5
94 Note: From the above program is that the user mentioned the step value as -5. For first time the loop starts from I = 10 then it checks for conditions and if it true then control transfer in to body of the loop. Then it reaches the end of the loop. Through next I statement is that the value of I is 10, that is decrement by 5 with the instruction given by step keyword. The again it checks for another condition and if it is true then again it starts execute the body of the loop. If the condition is false then it comes out of the loop and starts execute the next statement in a main program.
For I = 0 to 10 step 3
Msgbox” Executes the loop in order” Msgbox” The counter variable value increase by 3 for each execution”
Next i
Output Executes the loop in order The counter variable value increase by 3 for each execution Executes the loop in order The counter variable value increase by 3 for each execution
Executes the loop in order The counter variable value increase by 3 for each execution
Note: From the above program is that loop will execute or iterate till the value of I reaches 10 and for each time the step value is incremented by 3 and process for all values. Finally comes out of the loop when it reaches false condition.
6.4.3 Exit For statement
For loops can be exited before the counter reaches the end point. By using the Exit for statement, one can leave the for loop at ay point in the process, skipping over any code after the Exit for statement and resuming after the next statement in the code.
For statement is generally used in conjunction with some type of conditional code, such as the IF statement. The following is example program using Exit for statement.
95 Example For I = 0 to 100 If aary( I ) = “test” then Msgbox “found test” Exit for End if Next I
6.4.4 Nested For…Next
The term nesting is nothing but the For …next consist of another For loop as an inner loop of outer for loop.
Example For I = 0 to 4 For j = 0 to 3 Print” Inner loop” Next j Print “Outer loop” Next I
Output Inner loop Inner loop Inner loop Outer loop Inner loop Inner loop Inner loop Outer loop Inner loop Inner loop Inner loop Outer loop Inner loop Inner loop Inner loop Outer loop
96 Note: From the above VB program consist of nesting for loop concept. First it starts executes the outer loop for once then the condition is true then, control entered in to inner for ….next loop. Then again another condition is checked in inner loop, if it is true then entered in to body of inner loop. Once the inner gets active, then after the one iteration is over in inner loop then the control will again checks for another condition in inner loop. It repeats starts execution of inner loop completely. Then control is transferred to outer loop again. The second condition is checked again in outer loop then; control is transfer to inner loop again. This process repeat again and again till the condition becomes false in out loop. Totally from the above example is the outer loop executes for 4 times and inner loop checks for 3 times. Actually the 4 x 3 = 12 time the iteration will be occurred for final completion.
6.5 WHILE LOOPING
6.5.1 Do – While loop
Using the Do loop allows to repeat the code while or until a condition is met. Here we have two format of placing the condition in looping statements.
One is placing the condition at the beginning of the loop Another one is that placing the condition at the end of the loop
Example Here the condition is checked at the beginning of the loop Dim a as integer a = 1 Do while ( a > 5 ) Print( “While loop condition at beginning” a = a + 1 loop
Output While loop condition at beginning While loop condition at beginning While loop condition at beginning While loop condition at beginning
97 Note:
From the above example is that do while concept is that the condition is checked at the beginning of the loop. Here the value of a= 1 is initialized and starts executes. First it check the condition and if it false then it enter in to the loop. Each time the value of a = a + 1 is increment at the end of the loop. So final the condition reaches it true value means then it comes out of the loop. The control is transferred to next statement of the program.
Example
Here the condition is checked at the End of the loop
General format Do Statements Loop [ while (condition) ] Dim a as integer a = 1 Do Print( “Starts executes the loop before the condition executes”) Print( “while loop condition at End of the loop” a = a + 1 Loop while ( a > 5 )
Output Starts executes the loop before the condition executes While loop condition at End of the loop Starts executes the loop before the condition executes While loop condition at End of the loop Starts executes the loop before the condition executes While loop condition at End of the loop
Note:
From the above looping concept is that the condition is checked at the end of the loop. First it start initialize the value of a to 1. Then it starts executes the looping statement without considering the condition and after the execution the body of the loop. At the end of the loop the condition is checked if it is true it comes out the loop. If it is false then starts executed the same process for specified umber of times.
98 The key aspect of keeping the condition at the end is that the loop will execute at least once the looping statement will execute before the condition checks.
The following is a logical diagram for do loop concept for checking condition at the beginning of the loop.
If Yes Condition check
No Body of Loop
Statements After the body Of the loop
The following is a logical diagram for do loop concept for checking condition at the end of loop.
99 Body of Loop
No If Condition check
Yes
Statements After the body Of the loop
From the above logical diagram of the Do … loop concept is that have slight difference in placing the conditions. So from that the clear idea is that Do…loop is used for looping concept. But the placing the condition in area plays an important role in iteration purposes. Finally the key aspects under the Do…loop concept will solve the problems for much application in easy way.
6.5.2 Do – Until loop
The Do…until concept is also works like as the function of the while loop concept. But here the function is opposite of the while loop. Here it checks the condition until becomes false. If it gets true means it starts execute the loop again and again. Finally it comes out of the loop when its value becomes false.
100 General format Do until (condition) Statements Loop Example Dim a as integer a = 1 Do until ( a > 5 ) Print “Until loop condition at beginning” a = a + 1 Loop Output Until loop condition at beginning Until loop condition at beginning Until loop condition at beginning Until loop condition at beginning
Note: From the above example consist of until loop. Here it checks the condition at the beginning of the loop. First initialize the value of a = 1 then it checks for greatest value, if it is true then it comes out of the loop and starts executes the next statement in program. Otherwise the condition is false then it starts executes the body of the loop till it reaches the true value.
General format
Do Statements Loop until (condition) Example Dim a as integer a = 1 Do Print (“Until loop condition at the end of the loop” a = a + 1 Loop until ( a > 5 ) Output Until loop condition at the end of the loop Until loop condition at the end of the loop Until loop condition at the end of the loop Until loop condition at the end of the loop Note:
From the above visual basic program is that first initialize the variable a =1 is assigned. Then the control directly entered in to body of the loop without any conditions. After the execution of body statements then checks for conditions, if it is true then control is transferred to next statement of the program. If it is false the control is transferred to the beginning of the loop and precedes the same till the condition becomes true value.
101 LESSON-7 ARRAYS
7.1 Arrays 7.2 User defined data types 7.3 Data type conversions
7.1 ARRAYS
Normally the user uses Dim statement called as standard arrays and that of Redim is called as dynamic arrays. The static arrays that do not change when between calls to the procedure. Private and public keyword acts as an access specifier. The private – arrays private to the form or module. Public - arrays global to eh whole program. Type – for arrays of user – defined types.
Normally the Dim statement used to declare the standard arrays.
Dim [ with events ] varname [subscripts] as new type, varname as new type.
The with events keywords is valid only in class modules. This keywords specified that varname is an object variable used to respond to events triggered by an activeX object. The varname identifier is the name of the variable you are declaring. The use of [subscript] to declare the array.
The new keyword eables creation of an object. If the user uses the term new when declaring the object variable, a new instance of the object is created on first reference to it.
The type arguments specifies the data type of the variable ,which may be Byte, Boolean, Integer, Long, Currency, Single, Double, Date, String , Object, Variant. If any type is not used then the default is Variant type is used.
Some examples for standard arrays Dim strings(25) as string Dim twoarrays( 15, 10) as integer Dim test (35) Dim num (45) as integer.
102
Dynamic arrays
The user can use the Dim statement to declare an array with empty parenthesis to declare a dynamic array. Dynamic arrays can be dimensioned or redimensioned as with the ReDim statement.
Redim [ preserve ] varname [subscripts] as type , varname [subscript ] as type
The term preserve keyword to preserve the data in an existing array when user changes the size of the last dimensions. The varname argument holds the name of the arrays to re – dimensions. The subscript term specifies the dimensions of the array.
The type argument specifies the type of the array. The type may be Byte, Boolean, Integer, Long, Currency, Single, Double, Date, String, Object, Variant.
Example
Private sub form_click() Dim string1 as String Redim string1(15) string1 = “ welcome” Redim string1( 35) string1 = “Welcome to visual basic programming” End sub
Definition: An array is a consecutive group of memory locations that all have the same name and the same type. To refer to a particular location or element in the array, we specify the array name and the array element position number.
Arrays have upper and lower bounds and the elements have to lie within those bounds. Each index number in an array is allocated individual memory space and therefore users must evade declaring arrays of larger size than required. We can declare an array of any of the basic data types including variant, user-defined types and object variables. The individual elements of an array are all of the same data type. The Dynamic Array The programmer specifies the array type and the number of elements required by the array so that the compiler may reserve the appropriate amount of memory. Arrays may be declared as Public (in a code module), module or local. Module arrays are declared in the general declarations using keyword Dim or Private. Local arrays are declared in a procedure using Dim or Static. Array must be declared explicitly with keyword "As".
103 There are two types of arrays in Visual Basic namely: Fixed-size array: The size of array always remains the same-size doesn't change during the program execution. Dynamic array: The size of the array can be changed at the run time- size changes during the program execution. When an upper bound is specified in the declaration, a Fixed-array is created. The upper limit should always be within the range of long data type. Declaring a fixed-array
Dim numbers (5) As Integer
In the above illustration, numbers is the name of the array, and the number 6 included in the parentheses is the upper limit of the array. The above declaration creates an array with 6 elements, with index numbers running from 0 to 5. If we want to specify the lower limit, then the parentheses should include both the lower and upper limit along with the keyword. An example for this is given below.
Dim numbers (1 To 6) As Integer
In the above statement, an array of 10 elements is declared but with indexes running from 1 to 6. A public array can be declared using the keyword Public instead of Dim as shown below. Public numbers ( 5 ) as integer Multidimensional array Arrays can have multiple dimensions. A common use of multidimensional arrays is to represent tables of values consisting of information arranged in rows and columns. To identify a particular table element, we must specify two indexes: The first (by convention) identifies the element's row and the second (by convention) identifies the element's column. Tables or arrays that require two indexes to identify a particular element are called two dimensional arrays. Note that multidimensional arrays can have more than two dimensions. Visual Basic supports at least 60 array dimensions, but most people will need to use more than two or three dimensional-arrays. The following statement declares a two-dimensional array 50 by 50 array within a procedure.
Dim AvgMarks (50, 50)
104 It is also possible to define the lower limits for one or both the dimensions as for fixed size arrays. An example for this is given here.
Dim Marks (101 To 200, 1 To 100)
An example for three dimensional-arrays with defined lower limits is given below. Dim Details (101 To 200, 1 To 100, and 1 To 100)
Dynamic array There will be e a situation when the user may not know the exact size of the array at design time. Under such circumstances, a dynamic array can be initially declared and can add elements when needed instead of declaring the size of the array at design time. Dynamic arrays are more flexible than fixed-arrays, because they can be resized anytime to accommodate new data. Like fixed-sized arrays, dynamic arrays have Public (in code modules), module or local scope. Module dynamic arrays are declared using keyword Dim or Private. Local dynamic arrays are declared with either Dim or Static. e.g.: Dim dynArray ( )
The actual number of elements can be allocated using a ReDim statement. This example allocates the number of elements in the array based on the value of the variable, x.
ReDim dynArray (x + 1)
The Redim Statement can appear only in a procedure, which is an executable statement. The same way of declaration as used for fixed arrays is used for declaring Redim statements also. Redim is an executable statement. The lower an upper limit for each dimension can also be specified explicitly as in a fixed size array. An example for this is given below.
Redim FirstArray (4 to 12)
Each time on executing the ReDim statement, the current data stored in the array is lost and the default value is set. But if we want to change the size of the array without losing the previous data, we have to use the Preserve keyword with the ReDim statement. This is shown in the example given below.
ReDim Preserve dynArray (50 To 200)
When the Preserve keyword is used, only the upper limit of the last dimension in a multidimensional array can be changed. No other dimensions or the lower limit of the last dimension can be changed.
105 7.2 USER DEFINED DATA TYPES
Variables of different data types when combined as a single variable to hold several related information is called a User-Defined data type. A Type statement is used to define a user-defined type in the General declaration section of a form or module. User-defined data types can only be private in form while in standard modules can be public or private.
In Visual Basic, you can declare you own types or classes in a module or form. This will then behave as any other object in Visual Basic, except it only has properties. For example, the Screen object in Visual Basic exposes a number of properties, including FontCount and ActiveControl. These can be accessed by entering Screen. Font Count. You can create a custom version of this, which will allow you to define various elements that can store values. For example: Type Employee Record ' Create user-defined type. ID As Integer ' Define elements of data type. Name As String * 20 ' Fill with 20 spaces Address As String * 30 ' Fill with 30 spaces Phone As Long Hire Date As Date End Type
This user-defined type has 5 properties. At the moment you cannot access them, as Visual Basic requires that you declare another variable that is referenced to this user-defined type: Dim MyRecord As EmployeeRecord Note that if you want to declare a Type in a form, it must be declared as private. So, the following code fills a few values into this user-defined type: Private Type EmployeeRecord ' Create user-defined type. ID As Integer ' Define elements of data type. Name As String * 20 ' Fill with 20 spaces Address As String * 30 ' Fill with 30 spaces Phone As Long HireDate As Date Private End Type
106
' Reference variable to user-defined type Dim MyRecord As EmployeeRecord ' Declare variable.
' Comment1_Click event. Sub Command1_Click() ' Assignment to EmployeeRecord variable must occur in a procedure.
MyRecord.ID = 12003 ' Assign a value to an element. MyRecord.Phone = 1813670690 End Sub A user defined type, or UDT, is a VB technique for defining a data type that exactly meets the needs of your program. A UDT can contain two or more individual data items that can be of different types, such as String and Integer. A UDT can even contain other UDTs and arrays. You can also create arrays of a UDT. To define a UDT, use the Type...End Type statement, which must appear in the declarations section of a code module. Within the statement, you define the individual items, or members, that the UDT will contain. Here's an example of a UDT you might create for keeping track of employee data: Public Type Employee FirstNameAs String LastName As String DateOfHire As Date Salary As Currency EmployeeNumber As Integer End Type
Once you define the type, you can create instances of it just like any other data type, like so: Dim OneEmployee As Employee Dim AllEmployees(500) As Employee
To access the members of a UDT, you use the Name.Member notation. Here are some examples: OneEmployee.FirstName = "Jack" OneEmployee.LastName = "Sprat" AllEmployees(1).FirstName = "Maria" AllEmployees(1).LastName = "Sanchez"
107 Nesting UDTs can be useful in some situations. Here's an example: Public Type Person FirstNameAs String LastName As String End Type
Public Type Employee Name As Person DateOfHire As Date Salary As Currency EmployeeNumber As Integer
End Type
7.3 DATA TYPE CONVERSIONS
Visual Basic functions either to convert a string into an integer or vice versa and many more conversion functions. A complete listing of all the conversion functions offered by Visual Basic is elucidated below.
Conversion To Function Boolean Cbool Byte Cbyte Currency Ccur Date Cdate Decimals Cdec Double CDbl Integer Cint Long CLng Single CSng String CStr Variant Cvar Error CVErr
108 A conversion function should always be placed at the right hand side of the calculation statement.
Common Data Conversions in Visual Basic Conversion Functions Example Integer ANSI to String Chr Chr(66) ' returns "B" Number to String Format, Str Format(99e2, "###,###") ' returns "9,900" Format(Now, "mmmm yyyy") ' returns Date to String Format "August 1999" DateValue, String to Date CDate("09/99") ' returns 09/1/99 CDate String to Number Val Val("-1.098e3") ' returns -1098
After you determine what kind of value a Variant variable or a control holds, you can convert that argument to its associated datatype. The conversion functions shown in Table and describe the conversions you can perform.
The data conversion functions.
Function Description Asc() Converts its string argument to the ASCII number that matches the first (or only) character in the string CCur() Converts the argument to an equivalent Currency datatype CDbl() Converts the argument to an equivalent Double datatype CInt() Rounds its fractional argument to the next highest integer CLng() Converts the argument to an equivalentLong datatype CSng() Converts the argument to an equivalent Single datatype CStr() Converts the argument to an equivalent String datatype CVar() Converts the argument to an equivalent Variant datatype Fix() Truncates the fractional portion Int() Rounds the number down to the integer less than or equal to its arguments Hex() Converts its numeric argument to a hexadecimal (base-16) value Oct() Converts its numeric argument to an octal (base-8) value
109 LESSON-8 OPERATORS
8.1 Operators 8.2 String functions 8.2.1 String handling functions 8.3 Date and time functions
8.1 OPERATORS
In each and every language concepts the operator plays an important role for execution of any expression or any statement. For example Operands (variables) A = b + c
Operator ( + ) From the above example is that, if any expression or any statement wants to evaluate the result or value means we need operator. So without the operator for any expressions, user can’t able to find the result for a particular expression. In given example is that user is assigning a value for b= 5 and c = 10.
To get the result we need + operator for complete evaluation.
Result is A = 5 + 10 The output is A = 15 (we need operator called “+”)
Example
Result = (grade1 + grade2 + grade3 / nostudents)
In visual basic evaluates the expressions in parenthesis fro left to right, using pairs of operands and their associated operator. So it adds first two grades together first. Instead of adding the final grade, it first divides that grade by nostudents, because the division operation has higher precedence than addition.
Consider the value is ( 4 + 10 / 2 ) =( 4 + 5 ) Result is 9 In general such expression are evaluated from left to right , when it comes to contest between two operators , the operator with the higher precedence is used first.
110
The following is table displays the information for operator and operator precedence.
Arithmetic operators
1. Exponentiation - ^ 2. Negation - -- 3. Multiplication and division - * , / 4. Integer division - \ 5. Modulus arithmetic - Mod 6. Addition and subtraction - + , - 7. String concatenation - &
Comparison operators
1. Equality - = 2. Inequality - <> 3. Less than - < 4. Greater than - > 5. Less than or equal to - < = 6. Greater than or equal to - > =
Logical operators
1. Not 2. And 3. Or 4. Xor 5. Equ 6. Imp 7. Ls
When expression contain operators from more than one category means that the arithmetic operators are evaluated first, comparison operators are evaluated next, followed by logical operators. All comparison operators actually all have equal precedence, which means they are evaluated in the left to right order in which they exist in expressions. The parenthesis operator precedence is also maintained.
8.2 STRING FUNCTION
In visual basic there are two kinds of strings are variable – length and fixed – length strings. The user has to declare the variable length string by following way Dim strvariable as String
111 A variable length string can contain up to approximately 2 billion characters, and it can grow or shrink to match the data you place in it.
Next is that the user has to declare the fixed – length string with the help of an asterisk character ( * ) followed by the strings length.
Dim strfixed as String * 10 From the above type of fixed length of string 10 characters. A fixed length string can contain 1 to approximately 64 K characters.
The following table consists of various strings handling function used for different purpose in visual basic string contents.
Strcomp Compare two strings StrConv Convert strings Format, Lcase, Ucase Convert to lowercase or uppercase Space, String Create string of repeating character Len Find length of the string Format Format a string Lset, Rset Justify a string InStr, Left, Ltrim, Mid, Right, RTrim, Trim Manipulate strings Option Compare Set string comparison rues Asc, Chr Work with ASCII and ANSI values
Example
Consider that a string variable A$ = “welcome to coimbatore” = len ( A$) The output is 21 (including the blank spaces) Thus the length function will count the each character and gives the output in numeric value. It includes the blank space, special symbols are also considered for counting the length of the string.
The following table consist of string function that are most common string handling function in visual basic string function.
Function Description Asc Returns the character code corresponding to the first letter in a string InStr Returns the position of the first occurrence of one string within another
112 InStrRev Returns the position of the last occurrence of one string within another. Join Lets you build a larger string out of smaller strings Lcase Converts a string to lowercase Left Finds or remove a specified number of character from the beginning of a string Len Gives the length of a string LTrim Removes spaces from the beginning of a string Mid Finds or removes character from the string Replace Allows you to replace one or more occurrence of as string inside another. Right Finds or remove a specified number of character from the end of a string RTrim Removes spaces from the end of a string Split Allows you to break up a string at specified places. Str Returns the string equivalent of a number StrComp Another way to do string comparisons StrConv Converts a string from one to another String Returns a repeated string of identical characters Trim Trims spaces from both the beginning and end of a string UCase Converts a string to uppercase
Sgn Function Sgn (number) - Returns a Variant of subtype Integer that represents the sign of a given number.
Shell Function
Shell(pathname[, window style])
Runs the executable program specified by the pathname argument and returns a Variant of subtype Double that represents the program's task ID. If Shell is unsuccessful, it returns zero. The optional window style argument determines the style of the window in which the shelled program runs.
113 Sin Function
Sin(number) - Returns a Double value that represents the sine of a given angle (as specified by the number argument).
SLN Function
SLN (cost, salvage, life) Returns a Double value that represents the straight-line depreciation of an asset when given its initial cost, salvage value at the end of its useful life, and life span.
Space Function
Space (number) Returns a Variant of subtype String that contains a number of spaces.
Spc Function
Spc (n)
Inserts a specified number of spaces (n) when writing or displaying text using the Print # statement or the Print method.
Sqr Function
Sqr(number) Returns a Double value that represents the square root of a given number.
Static Statement
Static varname[([subscripts])] [As [New] type] [, varname[([subscripts])] [As [New] type]
Declares one or more static variables, which retain their values as long as the program is running. The varname argument is the name of the variable, and the optional As [New] type indicates its data type. If the New keyword is used, then an implicit creation of the object is made. The optional subscripts are the dimensions of an array variable. Stop Statement Stop - Suspends program execution.
114 Str Function Str (number) Returns a Variant of subtype String that is a representation of a given number. StrComp Function StrComp (string1, string2[, compare]) Returns a Variant of subtype Integer that indicates the result of a comparison between two strings (string1 and string2). The optional compare argument specifies how strings are to be compared, with 0 for a binary comparison and 1 for a noncase- sensitive textual comparison.
StrConv Function
StrConv (string, conversion) Returns a Variant of subtype String that has been converted from an original string as specified by the conversion argument. The conversion argument can use several VB constants to specify the type of conversion, such as vbUpperCase, vbLowerCase, and vbProperCase.
String Function
String(number, character) Returns a Variant of subtype String that is of the length specified by number and is filled with a given character.
SYD Function
SYD(cost, salvage, life, period)
Returns a Double value that represents the sum-of-years' digits depreciation of an asset when given its initial cost, salvage value at the end of its useful life, life span, and period for which depreciation is calculated.
8.3 DATE AND TIME FUNCTIONS
Visual basic has many built – in function to read the information contained in the system clock about time, day and the year. The date function returns a date of eth form month – day – year (mm - dd – yyyy) for the current date.
115 By assigning a string to date in one of the following forms,
Date = “mm – dd – yyyy “ Date = “mm/dd/yyyy”
Where mm are numerals between 01 to 12, dd are days between 01 to 31 and yyyy are years between 100 to 9999.
The user can also read the time in the system clock or temporarily reset it with the time function. The time function returns an eight – character date of the form hh:mm:ss.
Example
Time = “hh” - sest the hour; minues and seconds are set to 0
Function Description
Now returns the date and time as stored in the system clock Date returns the current date Time returns the current time
The following is table displays the date expression to display information contained in number using format function.
Form Display Format(Now, “m/d-yy”) 1/1/99 Format(Now,”hh:mm”) 23:05 Format(Now, “hh:mm AM/PM”) 10:05 PM Format(Now,”hh:mm AM/PM mm/dd/yy”) 10:05 PM 05/04/99
Finally in general that the following table consists of various function in Date and Time functions.
Function Description Date Returns the current date from the system clock DateAdd Lets add a specified interval to a date DateDiff Lets subtract a specified interval from a date DateSerial Returns a date corresponding to the specified day, month, year DateValue Take a string and returns a date Day Tells you what day a string or number represents Hour Tells you what hour a string or number represents
116 Minute Tells you what minute a string or number represents Month Tells you what month a string or number represents Now Returns the current time and date Second Tells you what second a string or number represents Time Tells you the current time in the system clock TimeSerial Returns a variable of date type for the given time Weekday Tells you what day of the week a date corresponds to Year Tells you what year a date corresponds to
Formatting Dates and Times
Format (Now, “m/d/yy”)
Returns a format like this : [ (month)-(day)-(year) ] where the all values are in 2 digits. Example: (5-19-06)
Format (Now, “dddd, mmmm, dd, yyyy”)
Returns a format like this: [ (day of week)-(month in words)-(day)-(year) ] where the month is in alphabets , day is in numbers , year is in four digit number. Example: (Thursday, April, 15, 2006)
Format (Now, “d-mmmm”)
Returns a format like this: [ (day)-(month in words) ] where the day is in digits , and month is in words.
Example: (15 April)
Format (Now, “d-mmm-yy”) Returns a format like this : [ (day)-(month in words)-(year) ] where days , years are in numbers ( as discussed) and month is in 3 letter words.
Example: (15-APR-06)
Format (Now, “hh:mm AM/PM”) Returns a format like this : [ (hour of day)-(minute of hour)] where , hour of day is in AM./PM mode as AM/PM has been written in the format option.
Example : (08:30 PM) if you do not specify this , it will come in a format (20:30)
117 Format (Now, “h:mm:ss A/P”) Same as above, but with a little difference, here instead of AM / PM; A , P will appear Example : (08:30 P)
Format (Now, “d-mmmm h:mm AM/PM”) Returns a format like this : [ (day)-(month in words)-(hours)-(minutes)- (AM/PM) ] Example : (15 April 8:30 PM)
Date and time functions.
Function Description Date Returns the current date. DateSerial(intYr, intMo, Returns an internal date value for the three arguments. intDay) DateAdd(strIntrvl, intN, Adds the intN value to the date specified by dteDate for the dteDate) given strIntrvl. DateDiff(strIntrvl, dte1, Returns the number of time intervals (specified by strIntrvl) dte2) between the two dates. DatePart(strIntrvl, dteDate) Returns the strIntrvl portion of the dteDate. Now Returns the current date and time in the date format. Time Returns the current time. Timer Returns the number of seconds since midnight. TimeSerial(hour, min, sec) Returns the current date and time in the internal date format for the time specified. Most of the time your application simply needs to know the current date or time to display the date or time on a form or report. Use Date, Time, or Now (for both) to return the current date, time, or both. Note The returned value is the internal Date data type format Visual Basic uses for variables declared as Date data type variables. You can assign and work with dates returned from Date, Time, and Now by assigning them to and from variables declared as Date data type variables. When you print the value, Visual Basic respects your computer's International Windows settings and prints the date or time in your country's format. The serial date and time functions let you convert a three-part date into a date that matches the internal Date data type so that you can work with variables that hold dates you specify. For example, if you want to store the value July 18, 1998, in a Date data type variable named dteDue, you can do so like this:
118 dteDue = DateSerial (1998, 7, 18)
If the year falls within the 20th century, you can omit the 19 before the year. If you try to store a value that doesn't correspond to a proper date or time value, the IsDate() function will return False to let you know that a bad date or time appears in the Date data type variable. In a similar manner, TimeSerial() returns an internal Date data type when you specify the three time parts, like this: dteTimePaid = TimeSerial(14, 32, 25) ' Stores 2:32:25 P.M.
The time works on a 24-hour clock, so 14 represents 2:00 in the afternoon. The Date data type holds dates, times, and date and time values, so your Date variable will hold whatever date or time combination you send. The DateSerial() and TimeSerial() functions let you specify expressions inside their argument lists to manipulate specific date and time portion values. For example, the expression DateSerial(1998, 7, 18-31) returns the date 31 days before July 18, 1998. Therefore, you don't have to worry about the number of days in a month or anything else. Such calculations are useful for aging accounts receivable balances. Use an expression inside TimeSerial () to eliminate worry with going past midnight, as in this example: TimeSerial (14-20, 30, 16). Such an expression represents 20 hours before 2:30:16 p.m. DateAdd(), DateDiff(), and DatePart() require a special string interval value that comes from Table.The interval tells these date functions how to process the date argument.
Date and time interval string values.
Interval Description h Hour d Day m Month n Minute q Quarter s Second y Day of year w Weekday ww Week yyyy Year Suppose the user entered a date value into a control or variable and you needed to work with a date 30 days after that date to remind the user after 30 days that a project is due. You can add 30 days to a date value without worrying about days in each month or year changes (as would happen if the date fell in late December) by specifying the following
119 expression that adds 20 days to the date and returns another date 20 days in the future: DateAdd("d", 20, dteUserDate). You can subtract 20 days using a negative interval. Suppose you want the date one year from the user's date? Code this expression anywhere you need the future date in a year and you don't have to worry about leap year:
DateAdd ("yyyy", 1, dteUserDate).
The DateDiff () function uses Table interval string value to return the number of intervals between two dates. For example, the following expression returns the number of weeks between two date values: dateDiff ("ww", dteUser1, dteUser2). DatePart ("d", dteUserBDay).
Visual Basic includes three additional functions that strip off the day, month, and year values from a Date datatype variable: Day(), Month(), and Year(). If you want to work with the current year, you can strip off the year from the current date like this: intYear = Year(Date) ' Get this year
120 UNIT – IV Lesson – 9 9.1 Using Standard controls 9.1.1 Forms 9.1.2 Label 9.1.3 Text Box 9.1.4 Command button 9.1.5 Check box 9.1.6 Option button
Lesson - 10 10.1 Other controls 10.1.1 List box 10.1.2 Combo box 10.1.3 Picture box 10.1.4 Image controls 10.1.5 Scroll bars 10.2 Directory concepts 10.2.1 Drive List box 10.2.2 Directory List Box
Lesson – 11 11.1 Timer controls 11.2 Frame 11.3 Shape and Line controls 11.4 Control Arrays 11.5 Dialog boxes 11.6 Single Document Interface (SDI) 11.7 Multiple Document Interface (MDI) 11.8 Menus 11.9 Menu Editor 11.10 Menu Creation
121 LESSON-9 USING STANDARD CONTROLS
9.1 Using Standard controls 9.1.1 Forms 9.1.2 Label 9.1.3 Text Box 9.1.4 Command button 9.1.5 Check box 9.1.6 Option button
9.1 USING STANDARD CONTROLS
9.1.1 Forms
Forms are the names for windows in visual basic originally user will called windows under design forms, and the actual result when running a window, but common usage has named both forms. And you user can add controls to forms in the Integrated Development Environment (IDE).
In that IDE window, at the top of the form window is title bar, which displays the form’s title, as in default as form1. At the right in the title bar is the control box, including the minimizing, maximizing buttons and also the close button. These are controls the user takes for granted in most windows.
After the title bar comes the menu bar, if the user has created any menu in that form. If not the menu will not be displayed in the form. After the menu bar the toolbar will be placed in your form based on the user convenience.
The main area of the form is that area where everything takes place is called as client area. In visual basic codes work with controls in the client area and leave the rest of the form to visual basic.
122 The form window is used to design the different forms an application will contain an application can have one or more forms. And each form can have many controls or tool from toolbox that perform various function for user requirements. The forms window can be resized to whatever size is required.
As it is resized, its new size will be displayed in the right most co –ordinate section of the standard toolbar. The form window is an important part in IDE window. Through this form only the user can able to design any type of application and finally getting their objective. For each platform the work area is important one like the way the form window is an important one in visual basic application.
Setting the title bar text in form
In default the title value or text in the form will be named as form1. If the user wants to change the title value to the required name by using the property called caption option in property window.
Example: If the wants the form with the title value as “My First program”
123 Property b caption b My First program
The form comes with minimizing and maximizing button in default at the upper right corner of the form. If user doesn’t want the buttons means that click the property called control box set to false. The following form is displayed with out the button for usage.
Setting form’s border
To set a form’s border style with its border style property, following are the possible values for that property.
0 - None 1 - Fixed Single 2 - Sizable 3 - Fixed Dialog 4 - Fixed tool widow 5 - Sizable tool window
Adding toolbars to form
124 Toolbars provide buttons that corresponds to menu items and give the user an easy way to select the commands those items corresponds.
The following is the procedure to add toolbars in to your form for easy access of user operations.
1. Click Project b component to get the dialog. 2. Click Microsoft windows common controls box and click ok button 3. Double click the new toolbar tool in the toolbox. 4. Right click the toolbar and select the properties item. 5. Click buttons tabs in the property page and click insert button to insert a new button in to the toolbar. 6. Give the new caption and set key property to the button. 7. Add other buttons and close the property window. 8. Double the toolbar and ready to write the coding for each option in that toolbar.
Referring the current form
While using writing the coding related to form, the user has to use the form name for refereeing the form. For example
Form1. caption = “welcome’ Form1. height = 150 Thus the above format is used for changing the caption and height value. Instead of that name as form1 can be replaced as ME keyword is used for current form. Me. Caption = “welcome” Me. Height = 150 Note: Thus the ME is an implicit variable, always available and stands for the current object.
Measurement in Forms
The default measurements units of forms are twips, nut the project design board want the data entry- forms are look like real screen.
Get the dimensions of a forms client area with these properties
Scalewidth - The width of the client area Scaleheight - The height of the client are a
125 Scaleleft - The horizontal coordinate of upper left of client area. Sclaetop - The vertical coordinate of upper left of client area.
Get the overall dimensions of the form using these properties
Width - The width of the form Height - The height of the form Left - The horizontal coordinate of the form Top - The vertical coordinate of the form
The scale property to set forms
0 - User defined 1 - Twips 2 - Points 3 - Pixles 4 - Characters 5 - Inches 6 - Millimeters 7 - Centimeters
9.1.2 Label
Label tool
The label control is used to display text that the user wants. Use can use the control to display text that labels other parts of the form that have own captions. Despite their name, label controls are not static. User can change the text in a label at runtime by setting its caption property. This control will exist in toolbox, as second left in order of other tools.
126 To add labels
Simple click the tool, click and drag in the form. Another way is that simply double the tool in tools box, the label with default caption as label1 is appeared in the form. Then click the tool and select the caption property option and change the caption value to user requirements.
To change the size of the label use size handlers that appear around a label when you select it or use top, left, width and height properties.
In some situation user need to use the text box for displaying result, in such a cases user can omit the text box. Instead of that user can use label tool also.
Example A = val(text1.text) B = val(text2.text) C= A + B Label1. caption = val(C)
Formatting the text in labels
Label control properties are Autosize - makes the label size itself to fit the text WordWrap - Enables word wrap if lines of text are too long FontBold - makes the font bold FontItalic - makes the font Italic Fontname - Font style names FontStrikethru - It strike the content FontUnderline - It underline the contents
Aligning the text in labels
The align property of label tool using the following options
VbLeftJustify - 0 - text is left aligned vbRightJustufify - 1 - text is right aligned VbCenter - 2 - text is centered
127 9.1.3 Text Box The text box is the primary input method for getting input and displaying output in visual basic. Here name property is used for while writing coding for that tool.
Aligning the text box
The following types are the properties for aligning the text box are as follows 0 - Left justified 1 - Right justified 2 - Centered
Multiline
Click the text box in the form and go to property called multiline to true, converting a text box into a multiline text box, complete the word wrap. The following is the example form consists of text box and also the text box with mulitline option.
Adding Scrollbars to text boxes
In case of multiline texts used in text box the scroll bar is need for the processing. The scroll bar property will change the display setting for text box as follows
0 - None 1 - Horizontal 2 - Vertical 3 - Both
128 Note:
The scroll bar property is applicable only the property called multiline property also in state of true.
Thus the following sample window consist of that, one actual text box and the second text box have scroll property btrue and multiline b true.
Locking the text box
The term lock refers that the user cannot access the particular text box for some time period. Use the property called locked b true. This property makes the text box, that the user cannot enter the text into the text box except under your program control.
Disabling the text box
The user can disable text box by setting the Enabled b false. It means that the user can’t enter text in to text box; it also means the text in the box appears grayed. Disabling the better method to indicate that the control is nit accessible.
Accessing text in text box
The user can directly enter the input value to the text box for further processing. In some cases the user no need to enter the data directly in to the text box. Instead by help of the coding the user can assign the content to the respective text box exist in the form. Example
The following is the example consists of for have a text box. In that user is not typing the content or not giving input to the text box directly. Instead they are writing the coding, that if the user clicks the command button the content will appear in the respective text box for further processing.
129 Selecting and replacing text in text box
To work with the part of the text box, user select the text you want these three properties.
SelLenght - returns or sets the number of characters selected SelStart - returns or sets the starting point of selected text. SelText - returns or sets the string containing the currently selected text.
Creating password control
To hide the information in our program user can use the password control exist in visual basic. To convert a standard text box in to password box, assign some characters to the password char. Property b password = “ + “
130 The another example is that password for text box with the symbol is @ instead of using “ * “ .
9.1.4 Command button
Command button allows the user to simply click them to perform actions. When the user chooses the button, it not only carries out the appropriate action, it also looks as if it is pushed and released. Whenever the user clicks a button, the click event procedure is invoked. The code for the click event procedure can be placed to perform the desired action.
To add a command button to the form, these steps are followed
1. Double click the icon in toolbox. This will place a new command button in the form. 2. Right click on the control and get the properties option and modify its name to user requirements. 3. Change the properties caption = &test for user shortcuts 4. Now double the command button. Vb brings the user to code window and in that code window, user have to write the respective coding for further actions. 5. Finally execute the form by pressing F5 and the command button will perform the task properly for user conditions. By pressing F5 and the command button will perform the task properly for user conditions.
Setting button caption
After the button is added in to form then, click the property window and set the caption to user requirements. If not by writing coding also user can change the caption value for button.
131 Private sub form_load) Command1.caption = “click here” End sub
The above coding will affect the command button to user view as follows
Caption = “click here” is added to command button while eh form load event is activated.
Setting background and text color
To change the back color of the command button is that back color property b any color name and also style property b graphical one.
The colors available in visual basic are Button face, button shadow etc. and a palate of colors. And the user can mention the color name by having values like RGB (Red, Green, and Blue). The each color value range from 0 to 255.
Example Command1.backcolor = RGB(25, 100, 200) Command1.backcolor = RGB(2, 200, 10) Command1.backcolor = RGB(200, 0, 50)
To user can set the color of a button caption using the button fore color property. Example Fore color to the button at design time
Private sub form_load() Command1.forecolor = RGB(100, 50, 25) Not possible Note] The above concept of giving fore color is not possible in command button tool.
132 Setting button font style
To format the command button use property called b font. If the user clicks font option in property window user will get the following dialog box.
From the above dialog box user can make change or select the required options to make the command to formatting one.
Giving shortcut to key in buttons
The user can able to use the program or to execute the program without mouse operation means that shortcut is available while dealing with command buttons. The following procedure is that to access the shortcut for particular button 1. Select the button 2. Go to property option in caption 3. Type or include & symbol before the caption value 4. Then access the shortcut by using alt key + that particular alphabet
Example
Caption = “& Click here”
133 Short Cut to access the command button use ALT + C
Setting buttons tab order
To make your buttons easier to operate from keyboard use tab order available in visual basic.
TabStop - indicates if this button ca accept the focus when the user tabs into TabIndex - is the index of the current button in the tab order. Default - is true for one control on a form only.
Disabling and hiding the buttons
The use can disable the button by setting its enabled property to b false.
Example Private form_load() Comnad1.enabled = false End sub
To hide the button in a form use the following coding in form load event
Example Private form_load() Comnad1.visible = false End sub
Adding tool tips to buttons
134 The term tool tip is nothing but it display help information while the mouse pointer moves over the button. Example
The above example consists of tool tip for button, when the mouse is over the button. Coding is done in property btool tip b content (user wants)
9.1.5 Check box
Option button and check box are similar to the command button control. But making them fully functional in an application requires some additional programming.
A check box is like a light switch, it is either on or off. Option buttons work very mush the same way because they are either on or off. However, when two or more option buttons are on the same form, only one option can be on at one time. But the check box can able make operate or make use one more than one at a time.
The check box is examined its value by property b value as 0, 1, 2
Here the value 0 - Unchecked 1 - Checked 2 - Grayed
Working with check box
A check box offers an option for the user. It might appear by itself as follows in dialog box. In that dialog if the check box is clicked there will be a display check mark. If it is again clicked the check mark will disappear. It is two state value called on / off.
If the tick is appear in the check box means that the box is assumed to present for condition. If the tick mark is not present there means that the box is not included for condition.
The only advantage of using the check box is that the user can select more than one box to be considered for processing. But the option button is not applicable for this type of conditions.
135
Creating a Check box
Although the basic check box has been in almost every windows application there is a second type of check box that can be used by simply changing the style of the check box control. The two styles of check boxes are listed below as follows.
Standard check boxes use the familiar box that is either empty or contains a check mark. Graphical check boxes look just like a command button. However, when the checkbox is deselected, the button is up and when the check box is selected, the button is down.
The following shows the appearance of each of the two check box styles with actual and graphical type.
136
Standard check box Graphical Check box
Note:
The method for changing the standard check box to graphical check box is that, first property b style b graphical .Then select the down picture property and select one picture to display in the graphical check box.
Changing the appearance of standard checkbox
When using the standard check box style, there are several properties that can be modified to change its appearance.
Change the font properties for the caption Modify both the fore color and back color Create either a Flat or 3D look with the appearance property Choose the side of the box where the caption is to displayed The standard check box can be disabled y setting the Enabled property of the control to false. These properties allow customizing the look of any form that uses check boxes.
9.1.6 Option button
Working with option button
Visual basic also comes with the option button control for many purposes for users. This control lets the user select from one of several choices. However, unlike the check box, the user can select only one option button at a time. This type of interaction is the same as a multiple – choice test.
137 The way this control works, if the user selects another option button, the one that was selected will be deselected automatically and the new one will be selected.
Note
The above for consist of option button, this button also have two state on and off, but user can select only one option button at a time.
The option button has the same capabilities as a check box for controlling the appearance of a single option button. The option button also is displayed as either a standard button or as a graphical button as follows.
138
Standard button Graphical button
Note: As like check box, the option buttons also have two types. To change the standard option button to graphical type, first property b style b graphical. Then select the property b down picture and select any picture in to that location for displaying the picture in option button. In graphical type of option button has two state called up and down.
Setting option state
The value property for option button has true and false.
Example Private sub form_load() Option1.value = true Msgbox(“welcome to visual basic”) End sub
Option buttons groups using frames
The method to create button groups on the same form is to use a container control, which holds other control within its frame or border.
139
Any control that is placed within a container control will be treated as part of that container. When option buttons are added to a container, they will be treated as a single group of buttons in that container. The most common container control used with option buttons is the frame control. The frame control is used to group the different sets of option buttons. This allows the placement of as many different sets of option buttons on a single form as needed.
140 LESSON-10 OTHER CONTROLS
10.1 Other controls 10.1.1 List box 10.1.2 Combo box 10.1.3 Picture box 10.1.4 Image controls 10.1.5 Scroll bars 10.2 Directory concepts 10.2.1 Drive List box 10.2.2 Directory List Box
10.1 OTHER CONTROLS
10.1.1 List box
The List box and Combo box controls present a set of choices that are displayed vertically in a single column. The list box control occupies a specified amount of space on the form. If the number of items that are entered in the List box exceeds the value that can be displayed in the area of the box, scroll bars will automatically appear on the control, which can be scrolled up and down or left or right through the list. Users cannot enter data in the list; they can only select items, which will be manipulated by the application.
The simple List box
The simple list box control enables to display a list from which the user can select one or more items. To add items to the list box control, visual basic provides the AddItem method. The list will be initialized when the form is initially loaded by using form_load() subroutine.
The subroutine executes before the form is actually displayed. The following is the coding for adding items to list box.
Private Sub Form_Load() List1.AddItem ("Sirumugai") List1.AddItem ("Coimbatore") List1.AddItem ("Erode")
141 List1.AddItem ("Chennai") List1.AddItem ("Tirchy") List1.AddItem ("Madurai") List1.AddItem ("Mettupalayam") End Sub The coding will add the items to the list box and display the window as follows.
The following coding is added to the list box click () event routine to displays the selected item from the list box to the text box. Private Sub List1_Click () Text1.Text = List1.Text End Sub
Visual basic uses an index value to reference each item in the list. These are assigned in the order in which the items are added to the list. The index value starts at 0 and increases through the number of items in the list.
Two special properties are available to help the usage of the item in the list. Listcount () provides a current count of the items in the list. List Index () returns the index value of the currently selected item.
142 An item can be removed using the RemoveItem() method. This method requires knowing the item’s index value. For example to remove the fifth item in a list box, the code as follows
List1. remoeitem (4)
If all the items in a list are to be removed, visual basic offers the clear method, which invokes as
List1.clear () If the user wants to select more than one data item from the list, the control has a Multi – Select property that enables the users to press CTRL key and select more than one item at a time.
Note: The data items placed in the list is not in order. So to make it in order use the property name sorted that when set to true causes visual basic to reorder the list after each add or remove operation. This means that the items can be added to the list in any order, and they are stored in the list in proper alphabetical order.
10.1.2 Combo box
The combo box control also contains multiple items but occupies less space on the screen. The combo box control is an expandable list box control; the user can expand it to make a selection and retract it after the selection is made. The real advantage of using combo box control is that the user can enter a new data to the list, rather than being forced to select only the items listed.
The combo box has three formats that can be chosen from when adding this control to the form.
Drop down combo box - style - 0 Simple combo box - style - 1 Drop down List combo box - style - 2
Drop down combo box
A drop down combo box can be created by adding a combo box to the form. The drop down combo box style is 0. The default is 0 formats. The difference between the list box and combo box is that this combo box takes up less room and displays the list items, only when called upon. The following is example for drop down combo box.
143
Simple combo box
To get the simple combo box is that style property b 1. By default simple combo box do not display their list box. In order to display the list box, the height property of the simple combo box control must be increased to a higher value. However the list needs to be shown all the time to allow the user to enter new values.
Note: The important one is that the height property is to be increased to maximum, based on the number of item exist in the simple combo box.
144 The Drop – Down List combo box
The only difference between the drop – down list combo box and drop down combo box that user cannot add entries to the list or enter a value not on the list. The drop down list simple combo box can be created by adding a combo box t to the form and modifying the style property of the control to 2 - drop down list simple combo.
Note: The drop down list combo box in this type of combo box the new entry or new data item is not supposed to add in to the list at run time.
10.1.3 Picture box
Picture boxes are more complete controls than image controls. The user can load images in to picture box. The picture box acts as a container for other controls. First to load a picture in to picture box, we have two method one by property and another by coding. 1. Property b picture b locate a picture (path) 2. By writing coding as
Example
Private sub form_load () Picture1.picture = load picture (“Path of the picture “) End sub
145 The user wants picture box to resize itself to fit the picture you will load into it, set its Auto size property b true. The picture content to be refreshed when needed set its Auto redraw property b true. The picture box is very versatile and can display images from bitmap, icon, metafile, JPEG, GIF files. To adjust the picture box to contents use the properties like Left, Top, Height, and Width. The picture boxes have an align property is used place the picture box at top, bottom or on a side of the form. The possible values are 0 - Align none 1 - Align bottom 2 - Align left 3 - Align right
Handling picture box events
Responding to targeted mouse clicks in an image means creating a image map, and you can create one with a picture box. Picture boxes have click events, but click events handles only tell you that the picture box was clicked, not where it was clicked.
146 Example Private sub picture1_click () Statements End sub
The click event is useful if you want to use picture boxes as sort of image bearing buttons. However, if you want to know where in a picture box the user clicked the mouse, use Mouse down events. The picture boxes also support key events like KeyDown, KeyPress and etc.
10.1.4 Image controls
The image control uses fewer system resources and repaints faster than a picture box. However it supports only a subset of the picture box properties, events, and methods.
To install an image control, just use the image control tool in the toolbox. After adding the image control to your form, just set its picture property to the image file you wan to display.
By default, image controls shape themselves to the image you display; if you want to stretch the image to fit the image control and not the other way around, set the image controls stretch property to true.(default is false).
147 Note: The key feature of the image tool is that have stretch property b true, means that it make the picture in to compressed form to fit the size of the image tools.
10.1.5 Scroll bars
When user place a large document in the text box, only part of which is visible at once. Using scroll bars, users can manipulate the document, moving through it as you like. User can manipulate that document by dragging the small box in the scroll bar, which is called the scroll bars thumb.
In visual basic have vertical and horizontal scroll bars in the toolbox. If the user adds the tool in to the form, the use max, min properties to set the possible range of values user can set, then read the value property to get the controls setting to change event handler.
The following is the window consists of vertical and horizontal scroll frequently used in the visual basic.
After the scroll bar added in the form, first thing is that to set a range of possible values by default is 0 to 32767. The maximum value a scroll bar can be set to is stored in it’s by Max property, and the minimum value is set by min property.
Next is that the Largechange property is used when the user clicks the scroll bar itself, not the thumb and not tan arrow button. The same way is that when the user clicks an arrow button, the thumb moves by an amount stored in the Smallchange property. The small change property will applied in the design tie or at runtime.
The value property holds values that can be in the range spanned by the values in the min and max properties. When the user makes a change in a scroll bar, user will get the new setting from the value property when the change event is triggered.
148 Example
Private sub form_load () Vscroll.min = 1 Vscroll.max= 50 Vscroll.largechange = 25 Vscroll.smalchange = 2 Vscroll.value = 40 Hscroll.min = 1 Hscroll.max= 100 Hscroll.largechange = 20 Hscroll.smalchange = 1 Hscroll.value = 50
End sub By using enabled property is used to disable them by setting the property by false status. The user can make a scroll bar disappear by setting its visible property to false. Both the property is of two statuses called true and false.
Adding scroll bar to text boxes When the text box have multiline property is to true, then it says confirmed that text box have automatically the scroll bars will be added. Next is that what kind of scroll bars user want to add on the text box; are horizontal , vertical or both, by setting the scrollbar property to the options
vbSBNone - 0 no scrollbars (default) vbHorizontal - 1 Horizontal vbVertical - 2 Vertical vbBoth - 3 both vertical and horizontal
10.2 DIRECTORY CONCEPTS
10.2.1 Drive List box
Normally the user uses the common dialog file open and file save to get file name and file paths from the user, but sometimes they don’t want it. Consider for example users have a program where you want to let the user select files but don’t want to use the dialog boxes. In such similar cases user can use the visual basic controls called the drive list box and directory list box, and the file list box.
The drive list box tool appears as the seventh tool down on the right in the toolbox.
149 The user can get the currently selected drive in a drive list box by using its drive property, and when the user change the drive in that control, a change event is generated.
Example Sub drive1_change () Dir1.path = drive1.drive End sub
10.2.2 Directory List Box
The directory list box control displays directories as hierarchical set of folders. This control is one of the file controls that are intrinsic to visual basic; its tool appears as the eighth tool.
150 To add a directory list box a form, just use its tool in the tool box. The important property of the directory list box is the path property, which holds the path of the current directory .when the user changes the current path, a change event is generated. For example, when the user makes a change in a directory list box, dirt1 we can pass the new path to a file list box.
Example Sub dir1_change () File1.apth = dir1.path End sub
Creating and deleting directories
User can create a new directory with Mkdir statement and remove a directory with the Rmdir statement.
Example Private sub command_click () MkDir “ c:\test ” End sub
Private sub command_click () RmDir “ c:\test ” End sub Changing the directories To change the default directory, use ChDir. For example where we change the default directory to “path “ chdir.
Example
Private sub command_click () ChDir “ c:\test2 ” End sub
151 LESSON-11 TIMER CONTROLS
11.1 Timer controls 11.2 Frame 11.3 Shape and Line controls 11.4 Control Arrays 11.5 Dialog boxes 11.6 Single Document Interface (SDI) 11.7 Multiple Document Interface (MDI) 11.8 Menus 11.9 Menu Editor 11.10 Menu Creation
11.1 TIMER CONTROLS
One of the simplest and most misunderstood controls included with visual basic is the Timer control. This control can be used to provide any type of time – related processing within an application.
152 If Microsoft word or most other word processors are used, the user would have probably seen something called auto save. This is when the application will periodically save what the user is working on.
Only very little needs to be done when using the timer control. After it is placed on the form as like above form. It appears as a small icon that invisible in runtime. There are only three properties that should be modified.
The properties are The Name property The Interval property The Enabled property
As good programming practice, the timer should be named as something that related to its task, such as clock tick, if it will be used to update a clock display. To use the control, one needs only set the interval property to the number of milliseconds that the timer has to wait before executing the code in its timer event routine. When the ser interval time expires, the timer event is executed. The only way to turn off the timer is to set its enabled property to false.
Example Private sub form _load () Timer.interval = 5000 // 5000 = 5 seconds in milliseconds Timer.enabled = true End sub
Private sub timer_timer () If me.backcolor = &H800000F then Me.backcolor = vbRed Else Me.backclor = &G0000000F End if End sub
11.2 FRAME
The method to create button or picture box groups on the same form is to use a container control, which can hold controls within its frame or border. Visual basic comes with several container controls that can be used for thus purpose, including the following:
153 Frame Picture SSTab Shape
Any control that is placed within a container control will be treated as part of that container. When option buttons are added to a container, they will be treated as a single group of buttons in that container. The most common container control used with option is the frame control. This allows the placement of as many different sets of option buttons on a single form as needed.
Although the user can select only one option button from the set that is displayed on a form, probably there is a need to present several different groups of option buttons to the user.
To set the text that appears at upper left in a frame, you set the frame’s caption property and also you can change the caption at runtime by setting this property. User can make frames appear flat or 3D (by default) by setting their appearance property. And also user can give frames tool tips i.e the explanatory text that appears in a small yellow widow when the mouse cursor rests over a control by setting the tootip property.
154 Setting frame size and location
Setting a frame height and width is easy – just set the frame height and width properties at design time or runtime. User can set the frame location in its container with its left and top properties or by using its Move method.
Example Private sub command1_click () Frame1.move frame1.left + 1000 End sub
11.3 SHAPE AND LINE CONTROLS
The user uses the shape control at design time to draw shapes on a form or picture box. The shapes can draw are rectangles, squares, ovals, circles, rounded rectangles, and rounded squares.
At runtime user can access and change the shape control’s properties like left, top, width, height, backcolor, fillstyle or fill color and use the methods like move or refresh.
T o draw a shape using the shape control tool, which exist in visual basic toolbox. Simply click and draw any shape and using the shape property user can change the style or object to user requirements.
The shape property as follows
VbShapeRectangle - 0 (Default) VbShapeSquare - 1 VbShapeOval - 2 VbShapeCircle - 3 VbShapeRoundedRectangle - 4 VbShapeRoundedSquare - 5
155 The user can set the width of the shape’s drawing line with the borderwidth property and fill the shape using the Fillcolor and Fillstyle properties. The border style property lets you select the style of the shape’s drawing line, including using dots and dashes.
Line control
The line control and the shape control available in visual basic can be very effectively utilized to create very attractive graphical user interfaces.
A line control is a straight – line segment that is drawn at design time. The position, length, color and style of the line control can be positioned to customize the look of an application.
156 11.4 CONTROL ARRAYS
The controls in a control array share common properties but, just like an array, use an index to distinguish among them. This index parameter identifies the specific control and gives you the flexibility you will need to organize information at run time. Control arrays also were the traditional method of adding new controls to a form at runtime and are still useful for this task.
The following is an example consists of control array concept automatically generated in the visual basic application. Suppose if the user adds first one text box as text1 is the name of it. Then again adding the second text box with default name as text2, but if the user is trying to change the name as text1 means, the visual basic immediately displays the message box for control arrays. The following is the control array dialog box is displayed as follows
Note:
The key aspect in control array is nothing but, to add the thing in to the list done by Load command and to remove the thing from the list, is done by unload command.
157 11.5 DIALOG BOXES
The common dialog control can displays five different dialog boxes – open a file, save a file, set a color, set a font, and prints a document. Adding a windows common dialog control to your program is easy by following steps.
1. Select the project b component 2. Select control tab and select Microsoft common dialog control and click ok button 3. Double click the tool and add the add the code you want to open the dialog box and make use of values the user sets.
To displays various dialog boxes use the common dialog methods are as follows. Showopen - show open dialog box Showsave - show save as dialog box Showcolor - show color dialog box Showfont - show font dialog box Showprinter - show printer or print options dialog box Showhelp - invokes the windows help engine
The user can set the common dialog action property to do the same thing. Here are the values you can place in the action bproperty.
158 0 - No action 1 - Displays open dialog box 2 - Displays save as dialog box 3 - Displays Color dialog box 4 - Displays Font dialog box 5 - Displays Print dialog box 6 - Runs win help 32.exe
11.6 SINGLE DOCUMENT INTERFACE (SDI)
To switch to the Single document interface (SDI)
1. Choose tools b options 2. Click on the advanced tab 3. Select the SDI development Environment check box.
159 11.7 MULTIPLE DOCUMENT INTERFACE (MDI)
The MDI stands for multiple document interface for windows environment in which one widow, usually called MDI container or MDI parent form, contains many other windows, usually called child forms.
Multiple document interface frame windows can display multiple child windows inside them; in fact, the visual basic IDE itself is a Multiple Document Interface window. For example, if you already have a program based on a single form called Form1, and you want to make that into Multiple document interface (MDI) window inside MDI fame, follows these steps.
1. Add a new MDI form to the project using the Project b Add MDI form item. 2. Select MDIChild property of the form you want to use as the MDI child form to true. 3. Run the program; the form you have made into the MDI child form appears in the MDI form.
Note: The one of the nicest features of visual basic MDI forms is that the menus of the parent form change according to which child form has the focus. This lets work with specific menus for each child form. What happens is that the menu for the child form that has the focus appears on the menu bar of eh MDI parent form – replacing whatever menu was previously there. The user only sees the menu for the child form when that child has the focus.
160 Arranging MDI child windows:
The user could arrange the MDI child forms with their Left, Top, Width, and height properties, but there is an easier way user can use MDI form method called Arrange().
For example, if the user adds a menu item to an MDI for named say “Testarrange” and use the Arrange () method to arrange all the windows in the form in a cascade this way. Private sub testarrange () Me. arrange vbcascade End sub
11.8 MENUS
Designing the right kind of menus will make the application much more user – friendly. In VB user can build up to six levels of menus. Menus that contain submenu are usually called hierarchical menus. Using three levels is best for easy access of program, if more than the four levels it exceeds means that will leads you to confusion. The user knows that a sub menu lurks below a given menu item if there is a b following the menu item.
161 The above is an example for menu sample format for file menu exists in visual basic IDE window.
The menu names in a program appear in the menu bar – usually just under the title bar - and when the user selects a menu, that menu opens like an above menu.
Each menu usually contains items arranged in a vertical list. These items are often grouped into functional groups with menus separators, or thin horizontal rules. When the user select a menu item, that item appears highlighted; pressing enter ort releasing the mouse button opens that item. Menu item can also be disabled (also called grayed out). A disabled item is not accessible to the user and does nothing if selected.
Each item should have a unique access characters for users who choose commands with keyboards. The user reaches the menu or menu item by pressing ALT key and the access characters. The access characters should be the first letter of the menu title, unless another letter offers a stronger link, no two menus or menu items should use the same access characters.
11.9 MENU EDITOR
User can create menu in visual basic by using Menu editor window available by choosing tools b menu editor (ctrl + e) whenever form is showing. The following is the windows will displays the various options exist in menu editor window for menu creation.
162 The following are the various options exist in the menu editor window for various functions for different requirements of the users.
The options are 1. Caption text box 2. Name text box 3. Ok and cancel button 4. Index box 5. Shortcut box 6. Window List check box 7. Help context ID box 8. Checked check box 9. Enabled check box 10. Visible check box 11. Arrow buttons 12. Next button 13. Insert button 14. Delete button
Example
The user wants the menu based on the following condition are
Menu 1 Show b picture1, picture 2
Menu 2 Dimension b height b Increase and decrease Dimension bWidth b Increase and decrease
By using the above condition user first enter in to the menu editor window and then type the content in caption and name textbox. Then use the arrow keys for creating sub menus for main menu. If user needs any other options means that options will be used based on requirements. Base on above conditions the coding in menu editor and output menu is displayed in the following windows.
163 Coding done in menu editor
The output menu created in form
164 UNIT – V
Lesson – 12
12.1 Using Data controls 12.1.1 Data Access objects - DAO
Lesson - 13
13.1 Record set 13.1.1 Creating a Record set 13.1.2 Adding Records 13.1.3 Editing Records 13.1.4 Updating Records 13.1.5 Moving Records 13.1.6 Deleting Records 13.1.7 Sorting Records 13.1.8 Finding / Searching Records
Lesson – 14 14.1 Data Report 14.2 Data Environment 14.3 Report and Designer 14.4 Connection object 14.5 Command object 14.6 Data Report Controls
165 LESSON – 12 USING DATA CONTROLS
12.1 USING DATA CONTROLS
The database are exploring the difference between the Microsoft programming objects sets: Data Access objects (DAO), Remote data objects (RDO), and ActiveX Data Objects (ADO).
In Visual basic, three data access interfaces are available. They are
1. ActiveX Data Objects (ADO) 2. Remote Data Objects (RDO) 3. Data Access Objects (DAO)
A data access interface is an object model that represents various facets of accessing data. Using visual basic, one can control the connection, statement builders and return data for use in any application through program codes.
The reason for the existence of three data access interfaces in Visual basic is that data access technology is constantly evolving and each of the three interfaces represents state of the art at different times. The latest in the evolution is ADO, which features a simpler – yet more flexible – object model than either RDO or DAO. For new projects, it is preferable to use ADO as the data access interfaces.
Visual basic only supported DAO, which connected to the Microsoft Jet database engine i.e. the database engine in Microsoft access. Then come to that there are other databases types available, Microsoft created the open database connectivity ODBC standard and supported ODBC with Remote Data Objects in Visual Basic.
There are two ways to work with the DAO, RDO, and ADO object sets in Visual basic. The first way is working with special controls that support them; the data control supports DAO, the remote data control supports ODBC, and the ADO data control supports ADO. The user can use the controls to connect to and move through databases, but they don’t actually display data, but the bound controls handle directly in code.
The second way is working with the three database object sets directly in code, without controls like data control or the ADO data control. Next is that how to create and edit them with the visual basic visual basic manager tool. And examine the data control, remote data control and the ADO data control to connect to database.
166 Databases
The transition from a table on paper to one in a computer is natural; with a computer user can sort, index, update and organize large tables of data in an easy way. User can connect tables together, creating relational databases. Each individual data entry in a table, such as students name, goes into a field in the table. A collection of fields together, such as name and grade fields in table make up a record. Each record gets its own row in a table, and each column in that row represents a different field.
A database is a collection of one or more tables. In DAO, those collections are called the workspace, and in RDO, and ADO they are referred to as the data environment. One popular way is to use Structured Query Language (SQL) , is used to set up a query in which applied to a database gives you a record set.
The second type of database as well: relational databases. Relational data bases are called relational because they are set up to relate the data in multiple tables together. To make a table relational that certain fields to be primary keys and foreign keys. The primary key in a table is usually the most important one – the one you might use to sort on, for instance. The foreign key usually represents the primary key in another table, giving you access to that table in an organized way.
The date control
The data control enables you to move around in a database from record to record and to display and manipulate data from the records in bound controls. This control displays a set of arrow buttons the user can manipulate to move through a database, and the records from that database are displayed in bound controls. In many situation user can perform the data access operations using the data control – without writing any code.
Data bound controls automatically displays data from one or more fields for the current record, and the data control performs all operations on the current record. If the data control is made to move to a different record, all bound controls automatically pass any changes to the data control to be saved in the database. The data control then moves to the requested record and passes back data from the current record to the bound controls is displayed.
Visual basic uses data control properties to open selected databases, create a DAO database object, and create a Record set object. The data controls Database and Record set properties refer to those databases and record set objects and user can manipulate the data using those properties.
167 Direct Access Object
In visual basic fist started working with database, it used the Microsoft jet database engine, which is that Microsoft access uses. Using the jet engine represented a considerable advance for visual basic, because it works with all kinds of data formats in the fields of a database; text, numbers, integer, longs, single, doubles, dates, binary values, OLE objects, currency values, Boolean values, and even memo objects. The jet engine also supports SQL, for database programmers found attractive.
To support the jet database engine, Microsoft added the data control to visual basic and you can use that controls to open jet database (.mdb) files. Microsoft also added a set of Data Access Objects (DAO).
DBEngine - The jet database engine Workspace - An area can hold one or more databases. Database - A collection of tables. TableDedf - The definition of a table QueryDef - The definition of a query Record Set - The set of records that make up the result of a query Field - A column in a table Index - An ordered list of records Relation tables - Stored information about the specific relationship between tables.
Remote Data Object
Remote data object (RDO) connects to databases using ODBC. The user can set up the ODBC connections to databases using ODBC item in the windows control panel, and then use one of those connections with RDO objects. The remote data objects are designed in parallel with the data access objects.
The remote data control is instructed to move to a different row, all bound controls automatically pass any changes to the remote data control to be saved to the ODBC data source. The remote data control then moves to the requested row and passes back data fro the current row to the bound controls is displayed.
The remote data control behaves like the data control in most respects, with some differences. Here SQL property like data controls record source property cannot accept the name of a table by itself unless user populates tables collected.
168 ActiveX Data Object
ActiveX data objects (ADO) data access in database server through any OLEDB provider. ADO is intended to give you a consistent interface for working with a wide variety of data source, from text files to ODBC relational database to complex groups of databases.
The Microsoft implements connection to all those data sources is with the OLE db set of com interfaces, but that standard is a very complex one. A set of objects with properties, events and methods.
Connection - Access from your application to a data source is through a connection, the environment necessary for exchanging data. The connection object is used to specify a particular data provider and any parameters. Command - A command issued across an established connection manipulates the data source is some way. The command object lets ADO make it easy to issue commands. Parameter - Commands can require parameters that can be set before you issue the command. If user requires a debit from a charge account, user would specify the amount of money to be debited as a parameter in parameter object. Record set - if user command is a query that returns data as rows of information in a table, and then those rows are placed in local storage in record set object. Field - A row of a record set consists of one or more fields, which are stored in field objects. Error - Errors can occur when your program is not able to establish a connection, execute a command, or perform an operation, and ADO supports an error object to hold the resulting error. Collection - ADO provides collections, an object that contains other objects of a particular type. ADO provides four types of collections; the connection object has error collection, the command object has the parameters collection, the record set object has the fields’ collection, and the connection, command, record set, and fields objects all have properties collections. Events - ADO uses the concept of events, just like other interface objects in visual basic. There are two types of events: connection events where the commands are executed and connection start or end. Record set event used to report the progress of data changes
169 ADO also includes the remote data services (RDS), user can move data from a server to a client application or webpage, manipulate the data on the client ad return updates to the server in one round – trip.
The ADO data control is similar to the data control and the remote data control. The ADO data control is designed to create a connection to a database using Microsoft ActiveX Data Objects (ADO). At design time user create a connection by setting the connection string property to a valid connection string, and then set the record source property to statement appropriate to the database manger.
Use ca set the connection string property to the name of a file that defines a connection. User then connect the ADO data control to a data bound controls such as the grid, data combo, or data list control by setting its data source properties to the ADO data control. At the runtime user can set Provider, connection string, and record source properties to change the database.
Adding control to a program
In visual basic three data access object sets: DAO, ADO, and RDO. The first simplest method: connecting that database to a data control in a visual basic program and using that data control with data – bound controls.
The data control is the only intrinsic database control – in the toolbox. This control tool appears as the tenth tool down in the toolbox. After adding the tool to the form then give the name as caption property to the name of the database table user is working.
170 Opening a database with data control
To connect a data control to a database, set the data control database name property to the path and name of the access / jet database file user want to open. Users have to select the table you want to work with in that file with the data controls record source property. After connection database, the drop down list box for the record source property in the properties window.
To connect a text box to a data control, data source property to the name of the data control. To display a particular field in the text box, place that fields name in the text box data filed property.
12.1.1 Data Access objects - DAO
Working with DAO, user can use the database and record set data access objects in your procedures. The database and record set objects each have properties and methods of their own, and you ca write procedures that use these properties and methods to manipulate your data.
To open a database in DAO, users just open a database object or create a new one. This object can represent a Microsoft jet database (.mdb) file, or an ODBC database connected through the Microsoft jet database engine. When the database object is available, user create record set object and use that object’s methods like Movefirst and Movenext to work with the database.
DAO also supports a client / server connection mode called ODBC Direct ODBC direct establishes a connection directly to an ODBC data source, without loading the Microsoft jet database engine into memory. In the ODBC diect object model, the connection object contains information about a connection to an ODBC data source, such as the server name, the data source name.
DAO creating a database
In the Microsoft DAO object library, to add a reference to that library, select the project b reference menu item, select the Microsoft DAO object library and click ok to close the reference dialog box.
Now we can make use of the data objects in that library to create a new database using Create Database. Create database is a method of the DAO workspace object i.e. There are a collection of workspace objects in the DAO DB engine objects workspaces collection.
171 The following windows are that used for initial process for creating a database for further steps.
The following is the statement for creating a new database concept by using the given format
Set database = workspace .createdatabase (name, locale [options])
The following is the arguments for createdatabase
Name - a string up to 255 characters long that is the name of the database files that you are creating. It can be the full path and file name, such as c:\vb\text.mdb. The default extension is .mdb. Locale - A string that specifies a collating order for creating the database, like dblanggeneral and dblanggreek. The following are the possible settings for arguments. dbEncrypt - creates an encrypted database dbVersion10 - creates a database that uses the jet engine version 1 file format. dbVersion11 - creates a database that uses the jet engine version 1.1 file format. dbVersion20 - creates a database that uses the jet engine version 2 file format. dbVersion30 - creates a database that uses the jet engine version 3 file format.
172 Creating a table with TableDef object
The user can append the new table definition to a database by tabledef collection. After the creation of a new database with DAO, the DAO project can have to create a new table using the new table item in the file b menu.
From the above dialog box is that the user can enter name of the new table to create in the text boxes in the new table dialog box. User can also use the information to create a new tabledef object td, which we declare as a form –wide variable.
Dim td as tabledef Sub createtable () Set td = db.createtabledef(tableform.text1.text) Statements From the above code will help to create a new tabledef named called td.
Adding fields to a TableDef object
The user can use that objects createfield method to do that, passing method the name of the new field and a constant indicating that fields type
173 General format
Tabledef. Createfield (Field name, field type)
The following are the constant specifying the possible field types.
dbBigInt dbBinary dbBoolean dbByte dbChar dbCurrency dbDate dbDecimal dbDouble dbFloat dbGUID dbInteger dbLong dbLongBinary dbMemo dbNumeric dbSingle dbText dbTime dbTimeStamp dbVarBinary
The following things user has to specify the names they want to give new fields in the new table dialog boxes. Sub createtable () Set td = db.createtabledef (tableform. Text1.text) Set fields(0) = td.createfield(tableform.text2.text.dbtext) Statements
Adding an index to a TableDef object
Use can create an index with the Dao createIndex method. The createIndex method creates an index object, and you can make one of the fields in a table that table’s index with that index objects createfield method.
Dim dbindex as Index
174 Sample
Sub createtable () Set td = db.createtabledef (tableform. Text1.text) Set fields(0) = td.createfield(tableform.text2.text.dbtext) Statements
Set dbindex = td.createindex (tabelform.text2.text & “index”)
dbindex.fields.append index field td.indexes.append db index
Sample Code Sample of using ADO Stream object to access BLOB data from a MySQL database. 'CREATE CONNECTION OBJECT AND ASSIGN CONNECTION STRING Dim conn As ADODB.Connection Set conn = New ADODB.Connection conn.ConnectionString = "DRIVER={MySQL ODBC 3.51 Driver};" _ & "SERVER=127.0.0.1;" _ & "DATABASE=test;" _ & "UID=testuser;" _ & "PWD=12345;" _ & "OPTION=" & 1 + 2 + 8 + 32 + 2048 + 16384 conn.CursorLocation = adUseClient conn.Open
'CREATE TABLE FOR SAMPLE CODE conn.execute "CREATE TABLE files(" _ & "file_id SMALLINT UNSIGNED AUTO_INCREMENT NOT NULL PRIMARY KEY," _ & "file_name VARCHAR(64) NOT NULL," _ & "file_size MEDIUMINT UNSIGNED NOT NULL," _ & "file MEDIUMBLOB NOT NULL)"
OPEN RECORDSET FOR WRITING
Dim rs As ADODB.Recordset Set rs = New ADODB.Recordset
Dim mystream As ADODB.Stream Set mystream = New ADODB.Stream
175 mystream.Type = adTypeBinary rs.Open "SELECT * FROM files WHERE 1=0", conn, adOpenStatic, adLockOptimistic rs.AddNew mystream.Open mystream.LoadFromFile "c:\myimage.gif" rs!file_name = "myimage.gif" rs!file_size = mystream.size rs!file = mystream.read rs.Update mystream.Close rs.Close
OPEN RECORDSET TO READ BLOB rs.Open "Select * from files WHERE files.file_id = 1", conn mystream.Open mystream.Write rs!File mystream.SaveToFile "c:\newimage.gif", adSaveCreateOverWrite mystream.close rs.close
OPEN RECORDSET FOR UPDATE OF BLOB COLUMN rs.Open "Select * from files WHERE files.file_id = 1", conn, adOpenStatic, adLockOptimistic mystream.Open mystream.LoadFromFile "c:\updateimage.gif" rs!file = mystream.Read rs.Update mystream.Close rs.Close
OPEN RECORDSET TO READ UPDATED IMAGE rs.Open "Select * from files WHERE files.file_id = 1", conn mystream.Open mystream.Write rs!file mystream.SaveToFile "c:\newupdatedimage.gif", adSaveCreateOverWrite mystream.Close rs.Close
176 conn.execute "DROP TABLE files" conn.Close msgbox "Success! Check your C:\ directory for newimage.gif and newupdatedimage.gif"
ADO (ActiveX Data Object) data control
The ADO (ActiveX Data Object) data control is the primary interface between a Visual Basic application and a database. It can be used without writing any code at all! Or, it can be a central part of a complex database management system. This icon may not appear in your Visual Basic toolbox. If it doesn’t, select Project from the main menu, then click Components. The Components window will appear. Select Microsoft ADO Data Control, and then click OK. The control will be added to your toolbox.
The data control can be used to perform the following tasks: 1. Connect to a database. 2. Open a specified database table. 3. Create a virtual table based on a database query. 4. Pass database fields to other Visual Basic tools, for display or editing. Such tools are bound tools (controls), or data aware. 5. Add new records or update a database. 6. Trap any errors that may occur while accessing data. 7. Close the database. Data Control Properties: Align - Determines where data control is displayed. Caption - Phrase displayed on the data control. ConnectionString - Contains the information used to establish a connection to a database. LockType - Indicates the type of locks placed on records during editing (default setting makes databases read-only).
177 Recordset - A set of records defined by a data control’s ConnectionString and RecordSource properties. Run- time only. RecordSource - Determines the table (or virtual table) the data control is attached to. As a rule, you need one data control for every database table, or virtual table, you need access to. One row of a table is accessible to each data control at any one time. This is referred to as the current record. When a data control is placed on a form, it appears with the assigned caption and four arrow buttons:
The arrows are used to navigate through the table rows (records). As indicated, the buttons can be used to move to the beginning of the table, the end of the table, or from record to record. The Database Design 1. Open up MS Access (Start - Programs - Microsoft Access) 2. Pick "Start a blank database" from the wizard that pops up 3. Pick a spot to save the mdb file and a name for it (mine was "CDCollectionA.mdb") 4. You'll get to the following window, where you double click on "Create a table in design view:"
the database design main window 5. When you double click that "create table in design view" you get to this window:
178 The table design view window 6. You want to follow the following steps to get the table
1. Make a field called ArtistName whose type is Text 2. Make a field called AlbumTitle whose type is Text 3. Make a field called Tracks whose type is Number (just a long integer is cool enough) 4. Select the rows in the design view (as pictured above) that have ArtistName and AlbumTitle. 5. Right-click on that selection, and pick Primary Key from the menu you get. This will make both fields into primary keys. The idea is that they can be primary because you'll never have identical artist names and album titles. 7. Once you've got your table built, just close that window. You'll be automatically prompted to save changes to the table design and to give the table a name 8. Once that's all done, you can either add a couple entries to the database by double clicking the CDs table from the database design main window and inputting them manually.
Software Design 1. Go to the Project menu and select Components (near the bottom). You want to add two new controls to your project: o The Microsoft ADO Data Control (OLEDB) and o Hierarchical Flex Grid
2. First thing first, start up VB with a Standard Exe project
179
3. The following stuff to your main form: 1. Change the caption of your main form to something hip and jive ... 2. Add a Hierarchical FlexGrid to your form by picking the tool and drawing it on your main form. 3. Add an ADO data source control to the form using the tool and drawing on the form. Change its visibility property to False. 4. Add two frames to the form using the tool and drawing them on the form. Change for one frame: its caption to Add Entry its (name) to fraAddEntry Change for the other (second) frame: its caption to Remove Entry its (name) to fraRemoveEntry 5. Draw the following controls in the Add Entry frame (yes, actually in the frame): 1. A text box with the (name) txtArtistName 2. A label above that text box with the caption Artist Name 3. A text box with the (name) txtAlbumTitle 4. A label above that text box with the caption Album Title 5. A text box with the (name) txtTrackCount 6. A label above that text box with the caption Number of Tracks 7. A command button with the (name) cmdAddEntry and the caption Add this info 6. Now, to the Remove Entry frame, add the following controls: 0. A command button with the (name) cmdRemoveEntry and the caption Remove Selected 1. A label with the caption Select the entry you want to remove and click the button:
180 4. Now, the most complicated part is formatting the Hierarchical Flex Grid
1. the AllowBigSelection property was set to False 2. the AllowUserResizing property was set to 0 3. the FixedCols property was set to 0 while the FixedRows property was set to 1 (this is recommended for pretty displaying of stuff) 4. the FocusRect property was set to 0 5. the HighLight property was set to 1 6. the ScrollBars property was set to 2 7. the ScrollTrack property was set to True 8. the SelectionMode property was set to 1
5. In the form design window, double click the form, which should bring up the code window with a blank Form_Load() subroutine. o You'll notice this time that we do the data and database hookup in code instead of in the property sheet. o For the ConnectionString property of the ADO Data Control, you can build it in the property sheet. There's a wizard in there that will do it from scratch for you, but it's pretty annoying to surf through. That's why I just included this string instead (it was built in the wizard though) o You need two global variables, and they appear right above the Form_Load() method. o For the FlexGrid DataSource, note that the Set command/directive/whatever is used!! Here's the code:
Option Explicit
Dim MinHeight As Long Dim MinWidth As Long
Private Sub Form_Load()
// Set up the database connectivity for the ADO data control With Adodc1 ConnectionString = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=" & _ App.Path & "\CDCollection.mdb;Persist Security Info=False"
//‘the record source just tells the data control what and how //to pull out of the database. RecordSource = "select * from CDs order by ArtistName"
//Set the Flex Grid data source to be the ADO data control.
181 Set MSHFlexGrid1.DataSource = Adodc1 //set up the format string for the flex grid. MSHFlexGrid1.FormatString = "Artist Name | Album Title | Track Count" //Position all the controls happily and store the form minimum size MinHeight = Form1.Height MinWidth = Form1.Width Call Form_Resize End Sub
Private Sub Form_Resize()
//check to see if the form is getting too small (Note: this is just to avoid
If MinHeight > Form1.Height Then Form1.Height = MinHeight Exit Sub ElseIf MinWidth > Form1.Width Then Form1.Width = MinWidth Exit Sub End If
'//esize the flexgrid to fit nicely on the screen MSHFlexGrid1.Width = Form1.ScaleWidth MSHFlexGrid1.Height = Form1.ScaleHeight / 2
// resize the happy columns to look pretty (40% for each text column, 20% for Track)
MSHFlexGrid1.ColWidth(0) = 0.4 * MSHFlexGrid1.Width MSHFlexGrid1.ColWidth(1) = MSHFlexGrid1.ColWidth(0) MSHFlexGrid1.ColWidth(2) = MSHFlexGrid1.Width – (MSHFlexGrid1.ColWidth(0) * 2) - 60
fraAddEntry.Top = (Form1.ScaleHeight / 2) + 100 fraAddEntry.Height = (Form1.ScaleHeight / 2) - 150 fraAddEntry.Width = (Form1.ScaleWidth * 0.64) fraRemoveEntry.Height = (Form1.ScaleHeight / 2) - 150 fraRemoveEntry.Top = (Form1.ScaleHeight / 2) + 100 fraRemoveEntry.Width = (Form1.ScaleWidth * 0.36) - 100 fraRemoveEntry.Left = fraAddEntry.Width + 100 End Sub
182 Private Sub cmdAddEntry_Click() //add a new entry to our table.
With Adodc1.Recordset .AddNew !ArtistName = txtArtistName !AlbumTitle = txtAlbumTitle !Tracks = txtTrackCount .Update .Requery
End With
Private Sub cmdRemoveEntry_Click() //delete an entry from the database
With Adodc1.Recordset .Move (MSHFlexGrid1.Row - 1) ' we minus one because row zero is the header row .Delete .Requery End With
183 LESSON-13 RECORD SET
13.1 Record set 13.1.1 Creating a Record set 13.1.2 Adding Records 13.1.3 Editing Records 13.1.4 Updating Records 13.1.5 Moving Records 13.1.6 Deleting Records 13.1.7 Sorting Records 13.1.8 Finding / Searching Records
13.1 RECORD SET
13.1.1 Creating a Record set After defining the database table with DAO tabledef object, user can append that object to a database object, which adds that table to that database. User can use the openRecordset method to open a record set and start working with data.
Set recordset = database.openrecordset (source, type, options, lockedits) The arguments for openRecordSet Source - A string specifying the source of the records for the new recordset object. The source can be tablename, a query name, or an SQL statement that returns records. Type - Indicates the type of record set to open. Options - combination of constants that specify characteristics of the new record set. Lockedits - constant that determines the locking for recordset.
The following are the possible settings for type
dbOpenTable - Opens a table – type recordset object dbOpenDynamic - opens a dynamic – type recordset object, which is like an ODBC dynamic cursor.
184 dbOpenDynaset - opens a dynaset – type recordset object, which is like an ODBC keyset cursor. dbOpenSnapshot - opens a snapshot – type recordset object, which is like a ODBC static cursor. dbOpenForwardOnly- opes a forward ony – type recordset object.
The following are the possible settings for options
dbAppendonly - allows users to append new records to the recordset but prevents them from editing to deleting existing records. dbSQLpassthrough - passes an SQL statement to Microsoft jet connected ODBC data source for processing. dbSeechanges - generates a runtime error if one user is changing data that another user is editing. dbDenyWrite - Prevents other users from modifying or adding records. dbDenyRead - Prevents other users from reading data in table. dbForwardOnly - Creates a forward – only record set. dbReadOnly - prevents users from making changes to the record set. dbRunAsyn - Runs an asynchronous query dbExecDirect - Runs a query by skipping SQL prepare and directly calling SQLExecDirect. dbInconsistent - Allows only consistent updates.
The following are the possible settings for lockedits
dbReadonly - prevents users from making changes to the record set. dbPessimistic - uses pessimistic locking to determine how changes are made to the recordset in multi user environment. dbOptimistic - uses optimistic locking to determine how changes are made to the recordset in multi user environment. dbOptimisticvalue - uses optimistic concurrency based on row values. dbOptimisticbatch - enables batch, optimistic updating
185 13.1.2 Adding Records To add a new record to a Dao record set, you use the Addnew method. After you have updated the fields of the current record, you save that record to the database with the update method.
Example When the user clicks the add button in your Dao code, the daocode project, we execute the Addnew method on the program record set and clear the two data field text boxes.
Private sub commnad1_click () dbrecordset. Addnerw text1.text = “ “ text2.text = “ “ End sub
13.1.3 Editing Records In some situation is that the user adding new record to the database, due wrong input data, user wants to change in the existing data called editing. For such condition user wants to edit the existing data in whole database. To do that user use the Edit method like DAO code example
Example Privaate sub command_click () Dbrecordset.Edit End sub After users edit the data in the records fields i.e. by entering new data in the text fields in the dao code project. They must update the database with new data, and they do that in that sample project by clicking the update database button. That update button will update the content in existing database.
13.1.4 Updating Records
When the user changes the data in record or adds a new record, we must update the database to record that change, and you the record set update method to do that
186 General format Recordset.update ( [type [, force]] ) The following are the arguments for this function Type - constant indicating the type of update, as specified in settings. Force - Boolean value indicating whether or not to force the changes into the database, regardless of whether the data has been changed by another user.
Example Private sub commnad1_click () dbrecordset.fields (0) = text1.text dbrecordset.fields (1) = text2.text End sub After loading the data into current records fields, we save that record to the database using the update method.
Private sub command2 _ click () dbrecordset.fields (0) = text1.text dbrecordset.fields (1) = text2.text dbrecordset. Update End sub
Note: The term update is nothing but changing the existing data in to newer one for any data. But while updating the user must consider the data and what will happens due to changes in existing data. If not considering the whole data base data will leads to confusion and cause whole damage to original data in the database.
13.1.5 Moving Records
The move term is nothing but user can move the data record value from database to any other position. The move command performs in the following types 1. Move to first record 2. Move to last record 3. Move to next record 4. Move to previous record
187 To make the first record in a record set the current, the user use the Movefirst method. Here the user wanst to move to the first record when the user clicks appropriate buttons in DAO coding.
Example Private subcommand4 _ click () Dbrecordset.MoveFirst Statements End sub
After moving to the first record, we display that records fields in the two text boxes.
Private sub command5_ click () Dbrecordset.MoveFirst Text1.text = dbrecordset . fields(0) Tex2.text = dbrecordset . fields(1) End sub
To make the last record in a record set the current record, user use the Movelast method. Here we want to move to the last record when the user clicks the appropriate button in DAO coding.
Example Private subcommand6 _ click () Dbrecordset.MoveLast Statements End sub
After moving to the first record, we display that records fields in the two text boxes.
Private sub command7_ click () Dbrecordset.MoveFirst Text1.text = dbrecordset . fields(0) Tex2.text = dbrecordset . fields(1) End sub
188 To make to the next record in a record set, making that record the current record, user will use the MoveNext methiod. Here in DAO project coding is used to move the next record when the user clicks the appropriate button
Private subcommand8 _ click () Dbrecordset.MoveNext Statements End sub Here if we check for end of the record set with EOF property is true. We should move back one record.
Private subcommand8 _ click () Dbrecordset.MoveNext If dbrecordset.EOF then Dbrecordset.MovePrevious Statements End sub
If the record we have moved to is a valid record, we display its fields in the program into text boxes.
Private subcommand8 _ click () Dbrecordset.MoveNext If dbrecordset.EOF then Dbrecordset. MovePrevious Else Text1.text = dbrecordset.fields(0) Text1.text = dbrecordset.fields(0) End if End sub
To move to the previous record in a record set, making that record the current record, user use the MovePrevious method. In DAO coding will mopve to the previous record when the user clicks the appropriate button.
189 Private subcommand9 _ click () Dbrecordset.MovePrevious Statements End sub
If we have gone past the beginning of the record wet with the BOF property is true. We should move forward one record.
Private subcommand10 _ click () Dbrecordset.MovePrevious If dbrecordset.BOF then Dbrecordset.MoveNext Statements End sub On theother hand, if the record we have moved to is a valid record, we display its fields in the program for corresponding text boxes.
Private subcommand11 _ click () Dbrecordset.MovePrevious If dbrecordset.BOF then Dbrecordset. MoveNext Else Text1.text = dbrecordset.fields (0) Text1.text = dbrecordset.fields (0) End if End sub
13.1.6 Deleting Records To delete a record in a DAO record set, use the Delete method, and then you update the record set. For example when the user clicks the Delete button in our DAO coding. We clear the two text boxes text1, and text2, that display the data for the current record and delete that record.
190 Private sub command12_ click () Text1.text = “ “ Text2.text = “ “ Dbrecordset.Delete End sub
13.1.7 Sorting Records
To sort a record set, you can install the index you want to sort with in the record set index property. For example, user want to sort the record set in our DAO coding with the index we have created this way.
Example Sub sort _ click () Set dbindex = td.Indexes (0) Dbrecordset.index = dbindx.name Statements End sub
After the record set is sorted, we display the first record in the two text boxes given. Sub sort _click () Set dbindex = td.Indexes (0) Dbrecordset.index = dbindx.name Text1.text = dbrecordset.fields (0) Text2.text = dbrecordset.fields (1) End sub
13.1.8 Finding / Searching Records
User can search a record set with an index; just set its Index property to the index we want to search and then set its Seek property to the string we want to search for. When the user selects the search menu item in DAO coding method. We install the index based on the first field in the record set.
191 Private sub search_ click () Set dbindex = td.indexex (0) Dbrecordset.index = dbndex.name Searchform.Show End sub
After the user dismisses the search, we retrieve the text to search for that the text box and place that text in the record sets Seek property, along with the command “ = ” which indicates we want to find exact matches to the search text.
Sub searchTable () Dbrecordset.Seek “ =” . searchform. Text1. Text Statements End sub
Beside = , you can also search using <, > ,< =, >=. When the search is complete, we display the found record in the text boxes.
Sub searchTable () Dbrecordset.Seek “ =” . searchform. Text1. Text Text1.text = dbrecordset.fields(0) Text2.text = dbrecordset.fields(1) End sub
192 LESSON-14 DATA REPORT
14.1 Data Report 14.2 Data Environment 14.3 Report and Designer 14.4 Connection object 14.5 Command object 14.6 Data Report Controls
14.1 DATA REPORT
Using Crystal Reports 'Crystal Reports' is a popular third party package that is included with Visual Basic, which allows you to create reports for your application. The package consists of a designer - where you can design and test the reports, Crystal Reports API calls and Crystal Reports control.
Note: Crystal Reports is shipped and installed as part of the VB installation package except in VB6. This can be found in \common\tools\crysrep double click on crystl32.exe to install.
To access the Crystal Report Designer, select the Report Designer from the Add-In menu in the VB environment. Following is the sample screen for crystal report.
193 While you are in design mode you can draw and arrange the data fields on the report. This is done in a similar way to creating controls on a form in VB. Start the Crystal Reports Designer Create a new report by choosing File menu - New and the Create New Report dialog box will appear (see picture below)
Click on the Custom button to display the Choose Report Type and Data Type frames. Select the Custom Report and click on the Data File. Specify the location of the BIBLIO.MDB Access database Select which tables from the database you want. For this example we will need the authors table and the Title table. Check that the joins are correct in the Linking Export
194 Drag and drop the fields you want on to the report. So that it looks like the report above. Now if you run it by selecting Print Preview, you can see what the report looks like. Now save the report and we have a template that now can be used in VB. Note: Turn off the Save Data with report option if you want the data to contain new information each time the report is used. Going to the File menu, selecting Options and clicking on the Reporting Tab sets the option There are many options in the Crystal Reports and but one important thing to do is to get specific data. This is done by a selection formula (i.e. the Where clause of a SQL statement).
14.2 DATA ENVIRONMENT
Using the Data Environment Designer The Data Environment provides a way for you to handle multiple Connection Objects that are associated with your programming project. The Data Environment Designer (DED) provides you with a visual interface for managing an instance of the Data Environment. Through the DED you can add, modify and delete the connections to data sources within the project. In addition, the DED provides an easy method of creating the Command objects that provide the links to specific sets of records in the data sources identified by the Connection objects. Finally, the DED provides the simplest way of creating the parent/child queries that are necessary for use with the Hierarchical Flex Grid and with master/detail data screens.
195 The first step in using a Data Environment in your program is to add an instance in your project. You do this by selecting the Data Environment item from the More ActiveX Designers submenu of the Project menu. (You can also select this option from the Add button on the main toolbar.) This menu item adds an instance of the Data Environment to your project and opens the DED window, as
Figure 1: The Data Environment Designer.
If you look at the project references for your project, you will notice that adding the Data Environment adds a reference to the Microsoft Data Environment Instance 1.0 and to the Microsoft ActiveX Data Objects 2.0 Library, as shown in Figure 2. The Data Environment is based on ADO, and you will need some ADO code in many of your applications.
Creating a Connection in the Data Environment The DED starts out with a single Connection object in the Data Environment. This Connection object enables you to create a link to a single data source, such as a Jet
196 database or SQL Server data source. You set up the link to the data source by setting properties of the Connection object. Activity 1 walks you through the process of creating the link to a Jet database.
Activity 1 1. Start a new Standard EXE project. 2. Add a new Data Environment to the project by choosing the Add Data Environment item from the Project menu. If this option is not available, choose the Components item from the Project menu and click the Data Environment option on the Designers page of the Components window to make this item appear on the project menu. 3. Open the instance of the Data Environment in the project by double-clicking the object in the Project window. 4. Right-click the Connection1 objects in the DED and select Properties from the pop- up menu to bring up the Data Link Properties dialog box for the connection. 5. On the first page of the properties, select the Microsoft Jet 4.0 OLE DB Provider for the connection. 6. After selecting the provider, click the Connection tab of the Data Link Properties dialog box. This page of the dialog enables you to select the specific source of the data for the connection. The content of this page varies depending on the data provider that you need. For the Jet data provider, you select the name and path of the database to which you are connecting. You may also need to provide the security information for the database if it is secured. For this activity, select the Nwind.mdb database that comes with Visual Basic. 7. After selecting the database name, test the connection by clicking the Test Connection button on the dialog. This creates a temporary connection to the database to ensure that all necessary parameters have been specified correctly. If everything is OK, you should receive the "Test connection succeeded" message. Otherwise, you receive an error message describing the problem. 8. Close the dialog by clicking the OK button. Your connection to a database is now set up. 9. You will probably notice that the DED gives the first connection a default name of Connection1. To change this name, click the connection to the DED and type a new name, or change the Name property of the connection in the Properties window in Visual Basic.
197 14.3 REPORT AND DESIGNER
The Sample Database Consider the folllowing sample database used for creating data report. EMPLOYEE.MDB contains three tables: EmpMast, DeptMast, and JobMast. The tables are structured as follows:
EmpMast table: Field Name DataType Comments EmpNbr AutoNumber Primary Key. Uniquely identifies each employee in the database. EmpFirst Text (50) Employee's first name EmpLast Text (50) Employee's last name DeptNbr Number (Long Integer) Foreign Key to PK of DeptMast table. Identifies which department the employee works in. JobNbr Number (Long Integer) Foreign Key to PK of JobMast table. Identifies the employee's job. HireDate Date/Time Date the employee was hired HrlyRate Number (Single) Employee's hourly rate SchedHrs Number (Single) The number of hours per week the employee is scheduled to work.
DeptMast table: Field Name DataType Comments DeptNbr Number (Long Integer) Primary Key; uniquely identifies each department in the database. DeptName Text (50) The name of the department. Location Text (50) The department's location (could be a building, suite number, floor, etc.)
JobMast table: Field Name DataType Comments JobNbr AutoNumber Primary Key; uniquely identifies each job in the database. JobTitle Text (50) The job title (description). MinRate Number (Single) The minimum hourly rate that somebody working in this position is usually paid. AvgRate Number (Single) The average hourly rate that somebody working in this position is usually paid. MaxRate Number (Single) The maximum hourly rate that somebody working in this position is usually paid.
198 Designing the Reports
From the above databses the following two types of reports will be developed and named as : "Annual Salary Expenses by Department" and "Annual Salary Expenses by Job".
For the Annual Salary Expenses by Department report, you want to show various fields from the employee database tables grouped and subtotaled by department. You also want to show a grand total at the end of the report. A sketch of the design might look something like the following:
Annual Salary Expenses by Department
JOB WKLY HRLY EMP # EMP NAME # JOB TITLE HIRE DATE HOURS RATE ANN SALARY ------DEPT XXXX XXXXXXXXXXXXXXXX XXX XXXXXXXXXXXXXXX XXX XXXXXXXXXX XX/XX/XX XX.XX XX.XX $XXX,XXX.XX XXX XXXXXXXXXXXXXXX XXX XXXXXXXXXX XX/XX/XX XX.XX XX.XX $XXX,XXX.XX DEPT XXXX XXXXXXXXXXXXXXXXXXXXXXXX TOTALS: $XXX,XXX.XX . . .
GRAND TOTALS: $XXX,XXX.XX The design of the Annual Salary Expenses by Job report is similar, except that you want to show various fields from the employee database tables grouped and subtotaled by job. You might sketch the design as follows:
Annual Salary Expenses by Job
DEPT WKLY HRLY EMP # EMP NAME # DEPT NAME HIRE DATE HOURS RATE ANN SALARY ------
199 JOB XXX XXXXXXXXXXXXXXXX
XXX XXXXXXXXXXXXXXX XXXX XXXXXXXXXX XX/XX/XX XX.XX XX.XX $XXX,XXX.XX XXX XXXXXXXXXXXXXXX XXXX XXXXXXXXXX XX/XX/XX XX.XX XX.XX $XXX,XXX.XX JOB XXX XXXXXXXXXXXXXXXXXXXXXXXX TOTALS: $XXX,XXX.XX
GRAND TOTALS: $XXX,XXX.XX
The following is he step-by-step process for designing the first report, "Annual Salary Expenses by Department". Once that is done, it will be a simple matter to copy that report and modify it to create the Annual Salary Expenses by Job report. With the report designs in mind, open Crystal Reports (Report Designer) from the VB Add-Ins menu:
A registration form appears. Click the Cancel button.
200 From the Crystal Reports File menu, select New:
The Create New Report dialog box appears. Click the Standard button.
The Create Report Expert dialog box appears with the Step 1: Tables tab open. Click the Data File button:
The Choose Database File dialog box appears. Navigate to the directory where your database file resides, then click the name of the database file so that it appears under "File Name:". Click the Add button, then click the Done button.
201
Step 2: Links tab then appears, showing you a diagram similar to that of Access' Relationships diagram.
202 Step 3: Fields tab. The "3: Fields" tab initially looks like this:
Using the "Add ->" button, select the desired fields from the "Database Fields" listbox so that they appear in the "Report Fields" listbox. Select the fields based on the initial design. For fields that are involved in a primary key and foreign key relationship, only select one of those fields from either table (for example, select the DeptNbr field from either the DeptMast table OR the EmpMast table, but not both). Select the following Database Fields: Select DeptNbr and DeptName from the DeptMast table. Select EmpNbr From the EmpMast table. Skip down to the JobMast table and select the JobNbr and JobTitle. Jump back up to the EmpMast table and select the HireDate, HrlyRate, and SchedHrs. Your screen should look like this:
203
You can specify column headings by selecting each of the Report Fields in turn, and giving them a heading by typing the desired text in the "Column Heading:" textbox (by default, the column heading is the same as the field name). Specify the column headings as follows:
Report Field Column Heading DeptMast.DeptNbr Dept # DeptMast.DeptName Dept Name EmpMast.EmpNbr Emp # JobMast.JobNbr Job # JobMast.JobTitle Job Title EmpMast.HireDate Hire Date EmpMast.HrlyRate Hrly Rate EmpMast.SchedHrs Wkly Hours
Click the Formula button. The "New Formula" dialog box appears. Type EmpName in the textbox and click OK
204
The "Edit Formula" dialog box appears. In the "Formula text" area, type: TrimRight ({EmpMast.EmpLast}) + ", " + TrimRight ({EmpMast.EmpFirst} Your screen should look like this:
Note: Crystal Reports has its own formula syntax, which differs from the syntax of VB and Access expressions. You can scroll the "Fields", "Functions", and "Operators" listboxes above the Formula text entry area to see what's available. Also, instead of typing everything directly into the text entry area, you can double-click on a listbox selection and the text of that selection will appear in the Formula text box.
Step 4: Sort tab Select DeptMast.DeptNbr from the "Report Fields" list and click the "Add->" button. DeptMast.DeptNbr then appears in the "Group Fields" list. Repeat this process for @EmpName.
205
Step 5: Total tab. Within this Total tab, an inner tabbed dialog appears, with one tab for each field selected in the sort. On the "DeptMast.DeptNbr" tab, remove all items except "@AnnSal" from the Total Fields list, as shown below. What we are saying is that we want to print a subtotal for the annual salary every time there is a change, or break, in the department number.
Still in the step 5: Total tab, click the "@EmpName" tab and remove all items from the Total Fields list i.e We don't want to print subtotals after every employee name.
206
We don't need to do anything in tab 6, Step 7: Style tab. For the title, type "Annual Salary Expenses by Department".
Click the Preview Report button. At this time, the "Create Report Expert" is finished and you can't go back to it, but you can make any desired changes in the Crystal Reports interface. Following is the screen that is initially displayed after you click the Preview Report button from Step 7 of the Expert:
207
208 14.4 CONNECTION OBJECT
Visual Basic 6 obsoletes the previously used database access technology provided by Jet and provides a new one known as ADO or Active Data Objects. This technology allows users to access data easily from many existing databases (such as Access or Paradox) or from ODBC compliant databases like Oracle or MS SQL Server. Using ADO is quite simple and allows programmers to provide flexible database front ends to users that are reliable and include many features. As a VB6 programmer ADO is important to know as most commercial VB programming exercises involve providing a front end to some sort of database. Following are some of the key objects found in the ADO object model and some of their key methods and properties.
Connection Object This object represents an open connection to the data source. This connection can be a local connection (say App. Path) or can be across a network in a client server application. Some of the methods and properties of this object are not available depending on the type of data source connected to. Key Properties
Name Data Type Description
Defines in string form the location of the data source you wish to connect to. Key fields in the string you will use are the "Provider=" and the "Data Source=" fields. You may also use the "Mode=" field. See descriptions of those properties for a more detailed view of each one. Some examples of connection strings follow: ConnectionStrin Data String g Source=c:\test.mdb;Mode=Read|Write;Persist - Connects to an Access database with read/write/persist permissions driver={SQL Server) server=bigsmile;uid=sa;pwd=pwd;database=p ubs - Connects to an SQL Server database called bigsmile as user sa with password pwd to database pubs.
A string defining the provider of a connection object. An example follows: Provider String Provider=Microsoft.Jet.OLEDB.4.0 -This string connects to a MS Jet 4.0 compliant database (an Access DB for example.)
Mode connectModeEnum Sets (or returns) the permissions for modifying
209 data across the open connection. Available permissions include Read, Write, Read/Write, and various Share/Deny types.
Sets the location of the cursor engine. You can select client side or server side, for simpler CursorLocation cursorLocationEnum databases (like Access) client side is the only choice.
Time in seconds that a connection will attempt to ConnectionTimeout Long be opened before an error is generated.
Time in seconds that an command will attempt to CommandTimeout Long be executed before an error is generated.
Key Methods
Name Description
Close Closes an open connection.
Opens a connection with the settings in the Open Connection String property.
14.5 COMMAND OBJECT
A command object specifies a specific method you intend to execute on or against the data source accessed by an open connection.
Key Properties
Name Data Type Description
Defines the Connection conConnection as ActiveConnection object the command ADODB.Connection belongs to.
Contains the text of the command you want to execute against a data source. This can be a table name, a valid SQL string, or the CommandText String name of a stored procedure in the data source. Which one you use is determined by the CommandType property.
210 Defines the type of the command. The three most commonly used would be adCmdText, adCmdTable, and adCmdStoredProc. The setting adCmdText causes the CommandText string to be evaluated as an SQL string. The setting adCmdTable causes CommandType commandTypeEnum the CommandText string to be evaluated as a table name and will return the all of the records and columns in a table. The setting adCmdStoredProc causes the CommandText string to be evaluated as a stored procedure in the data source.
Key Methods
Name Description
Executes the query, SQL statement, or stored procedure Execute specified in the Command Text property and returns a Record Set object.
ADO and the Command Object
The place of the command object in relation to the other objects in the ADO object model. The command object can query the data source and return a RecordSet Object. By providing the name of a parameterized query, or the name of a table in the database, or a stored procedure, the command object can be used to execute instructions and also return the results of the execution. The picture shown next also shows that the Parameters collection and Parameter object are related to the Command object. While the command object can execute a query repeatedly, it can also execute multiple queries.
211
Properties and Methods of the Command Object
Provide a reference to ADO 2.8 library
Before looking at any of the ADO objects, it is necessary to add a reference to the ADO library. By default, it may already have been added (ADO2.1) and it will be necessary to change it to a version higher than 2.5. The following window may be accessed by clicking on the Components drop-down menu when you click the menu item Tools when you are in the Microsoft Visual Basic screen.
212
However, if you learn to use the command object right from the start, you'll find that it makes manipulating recordsets much simpler and gives you more options. First, you must create the command object. You do this with the following piece of code:
'Create Command Object Dim objCmd 'Declare the command variable Set objCmd = Server.CreateObject("ADODB.Command") Set objCmd.ActiveConnection=objConnect objCmd.CommandType = adCmdText
213 Note that you set the command object's ActiveConnection property to your connection object, which you created above. Also note that, in this case, our CommandType is text. This allows us to send SQL commands directly to the database server. If you are using SQL Server as your database, the other command types may prove useful, but for most third party databases, such as Oracle or Informix, you are best off sticking with adCmdText.
Also note that adCmdText is a constant. The numeric equivalent is 1. The ADO constants are in a file called adovbs.inc. If you have not already included this file in your current page, locate it copy to your web directory and rename it adovbsinc.asp. Finally, add this line to the very top of your ASP page:
The reason for renaming it is for security purposes -- malicious users can more easily access a file on your server ending in .inc than one ending in .asp. Although this file is rarely changed and most ASP developers know its contents, it's just good practice not to have any of your code visible to web users.
14.6 DATA REPORT CONTROLS
One way of creating a data report is to: 1. Create a Data Environment designer containing a hierarchy of Command objects. 2. Set the DataSource property of the Data Report designer to the Data Environment designer. 3. Set the DataMember property to the topmost Command object. 4. Right-click the Data Report designer and click Retrieve Structure. After retrieving the structure, an appropriate number of Group headers and footers will be created, and each header/footer pair is assigned a name that corresponds to a Command object. 5. Drag Command objects from the Data Environment designer to the corresponding section on the Data Report designer.All of the data fields contained by a Command object are automatically created on the data report as TextBox controls on the section where the Command object is dropped. The DataMember and DataField properties of each TextBox are set in accordance with the Command object and its data fields.
214 6. Drag TextBox controls from the section where each was created onto a different section of the Data Report designer. 7. Add Function controls as needed to the report. When the data report is bound to a data environment, the rules for placement of controls on the report are not immediately apparent. This topic explains how the hierarchy created in the data environment relates to the system of group headers and footers constructed in the data report.
Hierarchy versus Headers, Footers, and Detail
The following picture shows a schematic view of the Data Environment designer with four Command objects, each in a parent/child relationship with at least one other command. The data fields that belong to the table are not shown.
The Data Report designer, on the other hand, is constructed as a series of sections. And each section can be categorized into one of four types: Report header/footers, Page header/footers, Group header/footers, and the Detail section. For the purposes of instruction, we can disregard the Report and Page header/footer pairs. This leaves the Group headers/footers and the Detail section. The Detail section, the innermost section of the designer, corresponds to the lowest-level Command object. As you go up through the hierarchy, the Detail section is bracketed by pairs of sections, with each pair associated with a single Command object. The figure below correlates the Command objects with the sections:
215 Sections Corresponding to Command Objects
Thus the figure shows that the hierarchy of the data environment actually corresponds to an expanding series of brackets, with the innermost (Detail) section corresponding to the lowest level of the hierarchy, and the outermost corresponding to the highest-level Command object.
Controls Can Be Placed in Any Section in a Lower Level
The placement of a control is governed by what section (or pair of sections) it belongs to. A control can be placed in the section where it originates, and in all sections that are at a level lower than itself. For example, if a control belongs to the Command1 section pair, it can also be placed in the section pairs for Commands 2, 3, and 4. A second example: A control that originates in section 3 can also be placed in section 4, but not in sections 1 and 2.
Placing the Function Control The Function control has three exceptions to the above guidelines regarding control placement. The Function control is not directly bound to the record set, as is the TextBox control. Instead, the Function control calculates its value as the report is generated. For this reason, a Function control can only be placed in Footer sections of the report. A second exception for the Function control: it can only be placed in any section pair that is one level above its own. For example, if the Command 3 object contains a Quantity field, you can place a Function control that sums the Quantity values onto the footer section for Command 2, or the footer section for Command 1. The third exception concerning the Function control is this: unlike the other data-bound control (the TextBox control), the Function control can be placed in the Report Footer section. When you do so, the scope of the control's calculation will be increased to include the whole report. For example, a Function control placed in the Report footer to calculate the sum of the Quantity field will calculate the sum of every Quantity control on the report.
216 The Exceptions: Grouping and Grand Total Aggregate With two exceptions, every Command object in the Data Environment corresponds to a pair of group headers and footers. The first exception occurs when you use the Grouping feature of the Data Environment designer.
Grouping Fields
When you create grouping fields, the Data Environment designer creates two folders under a single Command object. The first contains the grouping fields, and the second contains the Detail fields. Even though a new Command object is not created for the grouping fields, you must create a new group header/footer pair on the data report and this requirement qualifies it as an exception.
Grand Total Aggregate Fields
The second exception occurs when you create a Grand Total aggregate field in the data environment. As happens when creating a grouping field, a new folder is created for the Command object. The new folder contains any Grand Total aggregate fields created, and you must add a new group header/footer pair to the data report. he above is an example for menu sample format for file menu exists in visual basic IDE window.
The menu names in a program appear in the menu bar – usually just under the title bar - and when the user selects a menu, that menu opens like an above menu.
Each menu usually contains items arranged in a vertical list. These items are often grouped into functional groups with menus separators, or thin horizontal rules. When the user select a menu item, that item appears highlighted; pressing enter ort releasing the mouse button opens that item. Menu item can also be disabled (also called grayed out). A disabled item is not accessible to the user and does nothing if selected.
Each item should have a unique access characters for users who choose commands with keyboards. The user reaches the menu or menu item by pressing ALT key and the access characters. The access characters should be the first letter of the menu title, unless another letter offers a stronger link, no two menus or menu items should use the same access characters.
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User can create menu in visual basic by using Menu editor window available by choosing tools b menu editor (ctrl + e) whenever form is showing. The following is the windows will displays the various options exist in menu editor window for menu creation.
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