CS – 07 Programming in VB Block 1 :VB at a Glance Unit I: Introduction to VB Unit Contains 1.0 Program Design and Implementation 1.1 Design considerations 2.0 Introduction to Visual Basic 2.0 Evolution of Visual Basic 3.0 Hardware and Software Requirements of Visual Basic 4.0 Terms Often used in Visual Basic 5.0 An Application/Program in Visual Basic 6.0 Summary 1.0 Program Design and Implementation Software design is a process of problem-solving and planning for a software solution. After the purpose and specifications of software are determined, software developers will design or employ designers to develop a plan for a solution. It includes low-level component and algorithm implementation issues as well as the architectural view. A computer program is an organized list of instructions that, when executed, causes the computer to behave in a predetermined manner. Without programs, computers are useless. Therefore, programming means designing or creating a set of instructions to ask the computer to carry out certain jobs which normally are very much faster than human beings can do. The software requirements analysis (SRA) step of a software development process yields specifications that are used in software engineering. If the software is "semiautomated" or user centered, software design may involve user experience design yielding a story board to help determine those specifications. If the software is completely automated (meaning no user or user interface), a software design may be as simple as a flow chart or text describing a planned sequence of events. There are also semi-standard methods like Unified Modeling Language and Fundamental modeling concepts. In either case some documentation of the plan is usually the product of the design. A software design may be platform-independent or platform-specific, depending on the availability of the technology called for by the design. 1.1 Design considerations There are many aspects to consider in the design of a piece of software. The importance of each should reflect the goals the software is trying to achieve. Some of these aspects are: Compatibility - The software is able to operate with other products that are designed for interoperability with another product. For example, a piece of software may be backward-compatible with an older version of itself. Extensibility - New capabilities can be added to the software without major changes to the underlying architecture. Fault-tolerance - The software is resistant to and able to recover from component failure. 1 Maintainability - The software can be restored to a specified condition within a specified period of time. For example, antivirus software may include the ability to periodically receive virus definition updates in order to maintain the software's effectiveness. Modularity - the resulting software comprises well defined, independent components. That leads to better maintainability. The components could be then implemented and tested in isolation before being integrated to form a desired software system. This allows division of work in a software development project. Packaging - Printed material such as the box and manuals should match the style designated for the target market and should enhance usability. All compatibility information should be visible on the outside of the package. All components required for use should be included in the package or specified as a requirement on the outside of the package. Reliability - The software is able to perform a required function under stated conditions for a specified period of time. Reusability - the modular components designed should capture the essence of the functionality expected out of them and no more or less. This single-minded purpose renders the components reusable wherever there are similar needs in other designs. Robustness - The software is able to operate under stress or tolerate unpredictable or invalid input. For example, it can be designed with a resilience to low memory conditions. Security - The software is able to withstand hostile acts and influences. Usability - The software user interface must be intuitive (and often aesthetically pleasing) to its target user/audience. In many cases, online help should be included and also carefully designed. A software designer or architect may identify a design problem which has been solved by others before. A template or pattern describing a solution to a common problem is known as a design pattern. The reuse of such patterns can speed up the software development process, having been tested and proved in the past. Software design documentation may be reviewed or presented to allow constraints, specifications and even requirements to be adjusted prior to programming. Redesign may occur after review of a programmed simulation or prototype. It is possible to design software in the process of programming, without a plan or requirement analysis, but for more complex projects this would not be considered a professional approach. A separate design prior to programming allows for multidisciplinary designers and Subject Matter Experts (SMEs) to collaborate with highly-skilled programmers for software that is both useful and technically sound. 2.0 Introduction to Visual Basic A Computer cannot understand any persons spoken language. A spoken language such as English , French, is simply too general and ambiguous for computers to understand. Therefore, we must adapt to the machine and learn the computer language so that the computer can understand. This is where visual basic comes into it - when we type visual basic source code into the computer, the computer processes these statements into Visual Basic language. The statements in visual basic, however, do not have multiple meanings within the same context. Like the BASIC programming language, Visual Basic was designed to be easy to learn and use. The language not only allows programmers to create simple GUI applications, but can also develop complex applications As long as we are familiar with Windows 95, we can easily create applications with Visual Basic. We don't have to be a windows expert, but we should feel comfortable working with menus, the mouse and the windows interface. If we have opened, closed 2 and re-sized windows we should have the ability to make our own Visual Basic applications Visual Basic is a highly popular language in the commercial world because it allows for the rapid development of Windows based programs. VB is particularly strong at creating front ends for databases. This can be done in amazing time through the use of wizards A more limited version of Visual Basic is also included in several other Microsoft Applications such as MS Access. With VB 6, we can create any program depending on your objective. For example, you can create educational programs to teach science , mathematics, language, history , geography and so on. You can also create financial and accounting programs to make you a more efficient accountant or financial controller. For those who like games, can create those programs as well. Programming in VB is a combination of visually arranging components or controls on a form, specifying attributes and actions of those components, and writing additional lines of code for more functionality. Since default attributes and actions are defined for the components, a simple program can be created without the programmer having to write many lines of code. Performance problems were experienced by earlier versions, but with faster computers and native code compilation this has become less of an issue. Although programs can be compiled into native code executables from version 5 onwards, they still require the presence of runtime libraries of approximately 1 MB in size. This runtime is included by default in Windows 2000 and later, but for earlier versions of Windows like 95/98/NT it must be distributed together with the executable. Forms are created using drag-and-drop techniques. A tool is used to place controls (e.g., text boxes, buttons, etc.) on the form (window). Controls have attributes and event handlers associated with them. Default values are provided when the control is created, but may be changed by the programmer. Many attribute values can be modified during run time based on user actions or changes in the environment, providing a dynamic application. For example, code can be inserted into the form resize event handler to reposition a control so that it remains centered on the form, expands to fill up the form, etc. By inserting code into the event handler for a keypress in a text box, the program can automatically translate the case of the text being entered, or even prevent certain characters from being inserted. Visual Basic can create executables (EXE files), ActiveX controls, DLL files, but is primarily used to develop Windows applications and to interface web database systems. Dialog boxes with less functionality can be used to provide pop-up capabilities. Controls provide the basic functionality of the application, while programmers can insert additional logic within the appropriate event handlers. For example, a drop-down combination box will automatically display its list and allow the user to select any element. An event handler is called when an item is selected, which can then execute additional code created by the programmer to perform some action based on which element was selected, such as populating a related list. Alternatively, a Visual Basic component can have no user interface, and instead provide ActiveX objects to other programs via Component Object Model (COM). This allows for server-side processing or an add-in module. The language is garbage collected using reference counting, has a large library of utility objects, and has basic object oriented support. Since the more common components are included in the default project template, the programmer seldom needs to specify additional libraries. Unlike many other programming languages, Visual Basic is generally not case sensitive, although it will transform keywords into a standard case configuration and force the case of variable names to conform to the case of the entry within the symbol table entry.