DOCSLIB.ORG

Download PL / I Structured Programming Free Ebook

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text

Load more

PL / I STRUCTURED PROGRAMMING DOWNLOAD FREE BOOK Joan Kirby Hughes | 656 pages | 26 Jun 1986 | John Wiley and Sons Ltd | 9780471837466 | English | New York, United States PL/I structured programming A subset of the GY [19] document was offered to the joint effort by IBM and became the base document for standardization. The language is designed to be all things to all programmers. PC Magazine. With some conditions it is possible to complete executing an ON-unit and return to the point of interrupt e. Technical reports TR GY" written in Hursley from Control flow in imperative programming PL / I Structured Programming explicit : commands show how the computation takes place, step by step. This was not supported by many early IBM compilers. Object oriented programming languages are various but the most popular ones are class-based, meaning that objects are instances of PL / I Structured Programming, which also determine their types. Care is required to manage the use of initialization properly. Virtually no new development is being done in it. The logic and constraint paradigms are generally declarative as well. The structure statements are:. It has been used by academic, commercial and industrial organizations since it was introduced in the s, and is still used. Key Difference: The main difference between structured and unstructured programming language is that a structured programming language allows a programmer to code a program by diving the whole program into smaller units or modules. It means that the code will execute the instruction by instruction one after the other. The fields can be held in the preceding structure or, with some constraints, in the current one. The group is the unit of iteration. The first definition appeared in April This protects other parts of the program from modifications if the design decision is changed. Hidden categories: All articles with unsourced statements Articles with unsourced statements from February All articles with dead external links Articles with dead external links from May Articles with permanently dead external links Articles with unsourced statements from June Wikipedia articles needing clarification from April Articles with dead external links from April But it can be very rewarding. Each phase makes a single pass over the partially-compiled program, usually held in memory. So instead of noticing features that would make their job easier, Fortran programmers of the time noticed COBOL syntax and had the opinion that it was a business language, while COBOL programmers noticed Fortran syntax and looked upon it as a scientific language. Instead, these complexities are handled in the ON-units for the various file conditions. Examples are:. Changes and extensions were made through a Language Log that reached several thousand detailed points. Some Common Paradigms You should know these:. A statement is terminated by a semi-colon. A paradigm is a way of doing something like programmingnot a concrete thing like a language. Names may be declared to represent data of the following types, either as single PL / I Structured Programming, or as aggregates in the form of arrays, with a lower-bound and upper- bound PL / I Structured Programming dimension, or structures comprising nested structure, array and scalar variables :. Object Oriented Programming: Object oriented programming can be defined as a programming model which is based upon the concept of objects. Structured programming as a discipline is sometimes though to have been started by a famous letter by Edsger Dijkstra entitled Go to Statement Considered Harmful. Check out this Author's contributed articles. June They will provide the assignment to your specific requirements. Whichever version is used, it should not confuse anyone. The ADDR function computes such pointers, safely and machine independently. In object oriented programming, program is divided PL / I Structured Programming small parts called objects. In functional programmingcontrol flow is expressed by combining function calls, rather than by assigning values to variables:. At codeavail, our experts always deliver work before deadline so that any query can be resolved in time. Each has its own languages. And the de facto language continued to grow after the standard, ultimately driven by developments on the Personal Computer. The structured program consists of well structured and separated modules. PL / I Structured Programming and backtracking to find solutions i. PL/I structured programming Hidden categories: All articles with unsourced statements Articles with unsourced statements from February All articles with dead external links Articles with dead external links from May Articles with permanently dead external links Articles with unsourced statements PL / I Structured Programming June Wikipedia articles PL / I Structured Programming clarification from April Articles with dead external links from PL / I Structured Programming Archived from the original on April 15, This also allows the programmer PL / I Structured Programming check the module individually, before combining it with the program. The languages that support Structured programming approach are:. Object oriented programming languages are various but the most popular ones are class-based, meaning that objects are instances of classes, which also determine their types. Give It a Try and Place Order. Logic programming and constraint programming are two paradigms in which programs are built by setting up relations that specify facts and inference rulesand asking whether or not something is true i. April Why not? The phases are brought into memory from disk, one at PL / I Structured Programming time, to handle particular language features and aspects of compilation. Key Difference: The main difference between structured and unstructured programming language is that a structured programming language allows a programmer to code a program by diving the whole PL / I Structured Programming into smaller units or modules. OOP is based on the sending of messages to objects. In procedural programming, function is more important than data. This paradigm follows the top-down approach. Multiply a character string times a bit string and assign the result to a float decimal? PL / I Structured Programming some resources detailing several historic versions of the language. Writing code in comment? Writing code in comment? Free a controlled variable procedure parameter and reallocate it before passing it back? Please enter a valid number. Data can be allocated and freed within a specific area, and the area can PL / I Structured Programming deleted, read, and written as a unit. Proposals to change the base document were voted upon by both committees. This protects other parts of the program from modifications if the design decision is changed. Namespaces Article Talk. Programmers were sharply divided into scientific programmers who used Fortran and business programmers who used COBOLwith significant tension and even dislike between the groups. December However, this usage has become important for "pointer arithmetic" typically adding a certain amount to a known address. A statement is terminated by a semi-colon. You would write map square. This question is for testing whether or not you are a human visitor and to prevent automated spam submissions. Computational exception handling is enabled and disabled by condition prefixes on statements, blocks including ON-units and procedures. Cuff May The package construct consisting of a set of procedures and declarations for use as a unit. Further development of the language occurred in the standards bodies, with continuing improvements in structured programming and internal consistency, and with the omission of the more obscure or contentious features. Attention reader! Its main purpose to enforce a logical structure on the program being written to make it more efficient and easier to understand and modify. Just to code. It remained a minority but significant player. Order delivery You will receive a notification once your order is completed. What Code Should You Learn? With some conditions it is possible to complete executing an ON-unit and return to the point of interrupt e. An ON-unit may be terminated with a GO TO preventing a return to the point of interrupt, but permitting the program to continue execution elsewhere as determined by the programmer. This was anticipated in IBM before the first compilers were written. Additionally, unstructured programming languages allow only basic data types, such as numbers, strings and arrays numbered sets of variables of the same typewhich is not the case with structured programming languages. A declaration of an identifier may contain one or more of the following attributes but they need to be mutually consistent :. Learn About PL/I Programming: You Don’t Need An IBM Mainframe for This Obscure Language The intention was to create PL / I Structured Programming language which would have the scientific computing capabilities of Fortranand the PL / I Structured Programming data-processing power of COBOL. Many cases where pointer arithmetic might be needed involve finding a pointer to an element inside a larger data structure. Vowels March Compound assignment operators a la C e. Enterprise Systems Journal. It supports recursionstructured programminglinked data structure handling, fixed-pointfloating-pointcomplexcharacter string handling, and bit string handling. Virtually no new development is being done in it. Hoare representing ICL had
Recommended publications
  • Programming Paradigms & Object-Oriented

    Programming Paradigms & Object-Oriented

    4.3 (Programming Paradigms & Object-Oriented- Computer Science 9608 Programming) with Majid Tahir Syllabus Content: 4.3.1 Programming paradigms Show understanding of what is meant by a programming paradigm Show understanding of the characteristics of a number of programming paradigms (low- level, imperative (procedural), object-oriented, declarative) – low-level programming Demonstrate an ability to write low-level code that uses various address modes: o immediate, direct, indirect, indexed and relative (see Section 1.4.3 and Section 3.6.2) o imperative programming- see details in Section 2.3 (procedural programming) Object-oriented programming (OOP) o demonstrate an ability to solve a problem by designing appropriate classes o demonstrate an ability to write code that demonstrates the use of classes, inheritance, polymorphism and containment (aggregation) declarative programming o demonstrate an ability to solve a problem by writing appropriate facts and rules based on supplied information o demonstrate an ability to write code that can satisfy a goal using facts and rules Programming paradigms 1 4.3 (Programming Paradigms & Object-Oriented- Computer Science 9608 Programming) with Majid Tahir Programming paradigm: A programming paradigm is a set of programming concepts and is a fundamental style of programming. Each paradigm will support a different way of thinking and problem solving. Paradigms are supported by programming language features. Some programming languages support more than one paradigm. There are many different paradigms, not all mutually exclusive. Here are just a few different paradigms. Low-level programming paradigm The features of Low-level programming languages give us the ability to manipulate the contents of memory addresses and registers directly and exploit the architecture of a given processor.
  • A Feature Model of Actor, Agent, Functional, Object, and Procedural Programming Languages

    A Feature Model of Actor, Agent, Functional, Object, and Procedural Programming Languages

    Accepted Manuscript A feature model of actor, agent, functional, object, and procedural programming languages H.R. Jordan, G. Botterweck, J.H. Noll, A. Butterfield, R.W. Collier PII: S0167-6423(14)00050-1 DOI: 10.1016/j.scico.2014.02.009 Reference: SCICO 1711 To appear in: Science of Computer Programming Received date: 9 March 2013 Revised date: 31 January 2014 Accepted date: 5 February 2014 Please cite this article in press as: H.R. Jordan et al., A feature model of actor, agent, functional, object, and procedural programming languages, Science of Computer Programming (2014), http://dx.doi.org/10.1016/j.scico.2014.02.009 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. Highlights • A survey of existing programming language comparisons and comparison techniques. • Definitions of actor, agent, functional, object, and procedural programming concepts. • A feature model of general-purpose programming languages. • Mappings from five languages (C, Erlang, Haskell, Jason, and Java) to this model. A Feature Model of Actor, Agent, Functional, Object, and Procedural Programming Languages H.R. Jordana,∗, G. Botterwecka, J.H. Nolla, A. Butterfieldb, R.W. Collierc aLero, University of Limerick, Ireland bTrinity College Dublin, Dublin 2, Ireland cUniversity College Dublin, Belfield, Dublin 4, Ireland Abstract The number of programming languages is large [1] and steadily increasing [2].
  • The Machine That Builds Itself: How the Strengths of Lisp Family

    The Machine That Builds Itself: How the Strengths of Lisp Family

    Khomtchouk et al. OPINION NOTE The Machine that Builds Itself: How the Strengths of Lisp Family Languages Facilitate Building Complex and Flexible Bioinformatic Models Bohdan B. Khomtchouk1*, Edmund Weitz2 and Claes Wahlestedt1 *Correspondence: [email protected] Abstract 1Center for Therapeutic Innovation and Department of We address the need for expanding the presence of the Lisp family of Psychiatry and Behavioral programming languages in bioinformatics and computational biology research. Sciences, University of Miami Languages of this family, like Common Lisp, Scheme, or Clojure, facilitate the Miller School of Medicine, 1120 NW 14th ST, Miami, FL, USA creation of powerful and flexible software models that are required for complex 33136 and rapidly evolving domains like biology. We will point out several important key Full list of author information is features that distinguish languages of the Lisp family from other programming available at the end of the article languages and we will explain how these features can aid researchers in becoming more productive and creating better code. We will also show how these features make these languages ideal tools for artificial intelligence and machine learning applications. We will specifically stress the advantages of domain-specific languages (DSL): languages which are specialized to a particular area and thus not only facilitate easier research problem formulation, but also aid in the establishment of standards and best programming practices as applied to the specific research field at hand. DSLs are particularly easy to build in Common Lisp, the most comprehensive Lisp dialect, which is commonly referred to as the “programmable programming language.” We are convinced that Lisp grants programmers unprecedented power to build increasingly sophisticated artificial intelligence systems that may ultimately transform machine learning and AI research in bioinformatics and computational biology.
  • 15-150 Lectures 27 and 28: Imperative Programming

    15-150 Lectures 27 and 28: Imperative Programming

    15-150 Lectures 27 and 28: Imperative Programming Lectures by Dan Licata April 24 and 26, 2012 In these lectures, we will show that imperative programming is a special case of functional programming. We will also investigate the relationship between imperative programming and par- allelism, and think about what happens when the two are combined. 1 Mutable Cells Functional programming is all about transforming data into new data. Imperative programming is all about updating and changing data. To get started with imperative programming, ML provides a type 'a ref representing mutable memory cells. This type is equipped with: • A constructor ref : 'a -> 'a ref. Evaluating ref v creates and returns a new memory cell containing the value v. Pattern-matching a cell with the pattern ref p gets the contents. • An operation := : 'a ref * 'a -> unit that updates the contents of a cell. For example: val account = ref 100 val (ref cur) = account val () = account := 400 val (ref cur) = account 1. In the first line, evaluating ref 100 creates a new memory cell containing the value 100, which we will write as a box: 100 and binds the variable account to this cell. 2. The next line pattern-matches account as ref cur, which binds cur to the value currently in the box, in this case 100. 3. The next line updates the box to contain the value 400. 4. The final line reads the current value in the box, in this case 400. 1 It's important to note that, with mutation, the same program can have different results if it is evaluated multiple times.
  • Functional and Imperative Object-Oriented Programming in Theory and Practice

    Functional and Imperative Object-Oriented Programming in Theory and Practice

    Uppsala universitet Inst. för informatik och media Functional and Imperative Object-Oriented Programming in Theory and Practice A Study of Online Discussions in the Programming Community Per Jernlund & Martin Stenberg Kurs: Examensarbete Nivå: C Termin: VT-19 Datum: 14-06-2019 Abstract Functional programming (FP) has progressively become more prevalent and techniques from the FP paradigm has been implemented in many different Imperative object-oriented programming (OOP) languages. However, there is no indication that OOP is going out of style. Nevertheless the increased popularity in FP has sparked new discussions across the Internet between the FP and OOP communities regarding a multitude of related aspects. These discussions could provide insights into the questions and challenges faced by programmers today. This thesis investigates these online discussions in a small and contemporary scale in order to identify the most discussed aspect of FP and OOP. Once identified the statements and claims made by various discussion participants were selected and compared to literature relating to the aspects and the theory behind the paradigms in order to determine whether there was any discrepancies between practitioners and theory. It was done in order to investigate whether the practitioners had different ideas in the form of best practices that could influence theories. The most discussed aspect within FP and OOP was immutability and state relating primarily to the aspects of concurrency and performance. ​ ​ ​ ​ ​ ​ This thesis presents a selection of representative quotes that illustrate the different points of view held by groups in the community and then addresses those claims by investigating what is said in literature.
  • Unit 2 — Imperative and Object-Oriented Paradigm

    Unit 2 — Imperative and Object-Oriented Paradigm

    Programming Paradigms Unit 2 — Imperative and Object-oriented Paradigm J. Gamper Free University of Bozen-Bolzano Faculty of Computer Science IDSE PP 2018/19 Unit 2 – Imperative and Object-oriented Paradigm 1/38 Outline 1 Imperative Programming Paradigm 2 Abstract Data Types 3 Object-oriented Approach PP 2018/19 Unit 2 – Imperative and Object-oriented Paradigm 2/38 Imperative Programming Paradigm Outline 1 Imperative Programming Paradigm 2 Abstract Data Types 3 Object-oriented Approach PP 2018/19 Unit 2 – Imperative and Object-oriented Paradigm 3/38 Imperative Programming Paradigm Imperative Paradigm/1 The imperative paradigm is the oldest and most popular paradigm Based on the von Neumann architecture of computers Imperative programs define sequences of commands/statements for the computer that change a program state (i.e., set of variables) Commands are stored in memory and executed in the order found Commands retrieve data, perform a computation, and assign the result to a memory location Data ←→ Memory CPU (Data and Address Program) ←→ The hardware implementation of almost all Machine code computers is imperative 8B542408 83FA0077 06B80000 Machine code, which is native to the C9010000 008D0419 83FA0376 computer, and written in the imperative style B84AEBF1 5BC3 PP 2018/19 Unit 2 – Imperative and Object-oriented Paradigm 4/38 Imperative Programming Paradigm Imperative Paradigm/2 Central elements of imperative paradigm: Assigment statement: assigns values to memory locations and changes the current state of a program Variables refer
  • A Formal Component-Based Software Engineering Approach for Developing Trustworthy Systems

    A Formal Component-Based Software Engineering Approach for Developing Trustworthy Systems

    A FORMAL COMPONENT-BASED SOFTWARE ENGINEERING APPROACH FOR DEVELOPING TRUSTWORTHY SYSTEMS MUBARAK SAMI MOHAMMAD A THESIS IN THE DEPARTMENT OF COMPUTER SCIENCE AND SOFTWARE ENGINEERING PRESENTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY (COMPUTER SCIENCE) CONCORDIA UNIVERSITY MONTREAL´ ,QUEBEC´ ,CANADA APRIL 2009 °c MUBARAK SAMI MOHAMMAD, 2009 CONCORDIA UNIVERSITY School of Graduate Studies This is to certify that the thesis prepared By: Mr. Mubarak Sami Mohammad Entitled: A Formal Component-Based Software Engineering Approach for Developing Trustworthy Systems and submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy (Computer Science) (Computer Science) complies with the regulations of this University and meets the accepted standards with re- spect to originality and quality. Signed by the final examining committee: Chair Dr. External Examiner Dr. Nicholas Graham External to Program Dr. Jamal Bentahar Examiner Dr. Joey Paquet Examiner Dr. Juergen Rilling Supervisor Dr. Vasu Alagar Co-supervisor Dr. Olga Ormandjieva Approved Chair of Department or Graduate Program Director 20 Dr. Robin A.L. Drew, Dean Faculty of Engineering and Computer Science Abstract A Formal Component-Based Software Engineering Approach for Developing Trustworthy Systems Mubarak Sami Mohammad, Ph.D. Concordia University, 2009 Software systems are increasingly becoming ubiquitous, affecting the way we experience the world. Embedded software systems, especially those used in smart devices, have be- come an essential constituent of the technological infrastructure of modern societies. Such systems, in order to be trusted in society, must be proved to be trustworthy. Trustworthiness is a composite non-functional property that implies safety, timeliness, security, availability, and reliability.
  • Comparative Studies of Programming Languages; Course Lecture Notes

    Comparative Studies of Programming Languages; Course Lecture Notes

    Comparative Studies of Programming Languages, COMP6411 Lecture Notes, Revision 1.9 Joey Paquet Serguei A. Mokhov (Eds.) August 5, 2010 arXiv:1007.2123v6 [cs.PL] 4 Aug 2010 2 Preface Lecture notes for the Comparative Studies of Programming Languages course, COMP6411, taught at the Department of Computer Science and Software Engineering, Faculty of Engineering and Computer Science, Concordia University, Montreal, QC, Canada. These notes include a compiled book of primarily related articles from the Wikipedia, the Free Encyclopedia [24], as well as Comparative Programming Languages book [7] and other resources, including our own. The original notes were compiled by Dr. Paquet [14] 3 4 Contents 1 Brief History and Genealogy of Programming Languages 7 1.1 Introduction . 7 1.1.1 Subreferences . 7 1.2 History . 7 1.2.1 Pre-computer era . 7 1.2.2 Subreferences . 8 1.2.3 Early computer era . 8 1.2.4 Subreferences . 8 1.2.5 Modern/Structured programming languages . 9 1.3 References . 19 2 Programming Paradigms 21 2.1 Introduction . 21 2.2 History . 21 2.2.1 Low-level: binary, assembly . 21 2.2.2 Procedural programming . 22 2.2.3 Object-oriented programming . 23 2.2.4 Declarative programming . 27 3 Program Evaluation 33 3.1 Program analysis and translation phases . 33 3.1.1 Front end . 33 3.1.2 Back end . 34 3.2 Compilation vs. interpretation . 34 3.2.1 Compilation . 34 3.2.2 Interpretation . 36 3.2.3 Subreferences . 37 3.3 Type System . 38 3.3.1 Type checking . 38 3.4 Memory management .
  • Programming Languages

    Programming Languages

    Lecture 19 / Chapter 13 COSC1300/ITSC 1401/BCIS 1405 12/5/2004 Lecture 19 / Chapter 13 COSC1300/ITSC 1401/BCIS 1405 12/5/2004 General Items: Computer Program • Lab? Ok? • Read the extra credits • A series of instructions that direct a computer to perform tasks • Need to come to class • Such as? Who is the programmer? • Have a quiz / no books / use notes -> What is the big idea • School is almost over • Programming language is a series of rules for writing the instructions • • There are hundreds of computer programs – need-based! Reading Materials: Programming language • - Two basic types: Low- and high-level programming languages Miscellaneous: o Low-level: Programming language that is machine-dependent ° Must be run on specific machines o High-level: Language that is machine-independent ° Can be run on different types of machines Programming Language Low Level High Level Machine Assembly Language Language Procedural Nonprocedural Remember: Ultimately, everything must be converted to the machine language! Object Oriented F.Farahmand 1 / 12 File: lec14chap13f04.doc F.Farahmand 2 / 12 File: lec14chap13f04.doc Lecture 19 / Chapter 13 COSC1300/ITSC 1401/BCIS 1405 12/5/2004 Lecture 19 / Chapter 13 COSC1300/ITSC 1401/BCIS 1405 12/5/2004 Categories of programming languages o Nonprocedural language -> Programmer specifies only what the - Machine language program should accomplish; it does not explain how o Only language computer understands directly - Forth-generation language - Assembly language o Syntax is closer to human language than that
  • Functional Programming Functional Vs. Imperative Referential

    Functional Programming Functional Vs. Imperative Referential

    Functional vs. Imperative Referential transparency Imperative programming concerned with “how.” The main (good) property of functional programming is Functional Programming referential transparency. Functional programming concerned with “what.” COMS W4115 Every expression denotes a single value. Based on the mathematics of the lambda calculus Prof. Stephen A. Edwards (Church as opposed to Turing). The value cannot be changed by evaluating an expression Spring 2003 or by sharing it between different parts of the program. “Programming without variables” Columbia University No references to global data; there is no global data. Department of Computer Science It is inherently concise, elegant, and difficult to create subtle bugs in. There are no side-effects, unlike in referentially opaque Original version by Prof. Simon Parsons languages. It’s a cult: once you catch the functional bug, you never escape. The Joy of Pascal Strange behavior Variables program example(output) This prints 5 then 4. At the heart of the “problem” is fact that the global data var flag: boolean; flag affects the value of f. Odd since you expect function f(n:int): int In particular begin f (1) + f (2) = f (2) + f (1) if flag then f := n flag := not flag else f := 2*n; gives the offending behavior flag := not flag Mathematical functions only depend on their inputs end They have no memory Eliminating assignments eliminates such problems. begin In functional languages, variables not names for storage. flag := true; What does this print? Instead, they’re names that refer to particular values. writeln(f(1) + f(2)); writeln(f(2) + f(1)); Think of them as not very variables.
  • C++ Tutorial Part I : Procedural Programming

    C++ Tutorial Part I : Procedural Programming

    C++ Tutorial Part I : Procedural Programming C. David Sherrill School of Chemistry and Biochemistry School of Computational Science and Engineering Georgia Institute of Technology Purpose To provide rapid training in elements of C++ syntax, C++ procedural programming, and C++ object- oriented programming for those with some basic prior programming experience To provide a handy programming reference for selected topics To provide numerous, actual C++ code examples for instruction and reference Why C++? “Intermediate”-level language: allows for fine (low- level) control over hardware, yet also allows certain complex tasks to be done with relatively little code (high-level) Good for scientific applications: produces efficient, compiled code, yet has features that help one develop and maintain a complicated, large code (e.g., namespaces, object-oriented design) Recommended reading These notes were developed during my reading of “Sams Teach Yourself C++ in One Hour a Day,” 7th Edition, by Siddhartha Rao (Sams, Indianapolis, 2012). I recommend the book, it’s readable and to the point. A good mastery of C++ will probably require working through a book like that one, and doing some examples; notes like these only serve as a basic introduction or a quick review A Note on C++11 This was originally supposed to be C++0x, with the “x” filled in according to the year the new C++ standard was finalized (e.g., C++09 for 2009). However, the standard took longer than expected, and was only formalized in 2011. So, C++11 is what was formerly referred to as C++0x. As of 2013, the new C++11 standards are not yet fully implemented in many compilers.
  • Imperative Programming Languages (IPL)

    Imperative Programming Languages (IPL)

    Imperative Programming Languages (IPL) © Definitions: • The imperative (or procedural) paradigm is the closest to the structure of actual computers. • It is a model that is based on moving bits around and changing machine state • Programming languages based on the imperative paradigm have the following characteristics: The basic unit of abstraction is the PROCEDURE, whose basic structure is a sequence of statements that are executed in succession, abstracting the way that the program counter is incremented so as to proceed through a series of machine instructions residing in sequential hardware memory cells. The sequential flow of execution can be modified by conditional and looping statements (as well as by the very low-level goto statement found in many imperative languages), which abstract the conditional and unconditional branch instructions found in the underlying machine instruction set. Variables play a key role, and serve as abstractions of hardware memory cells. Typically, a given variable may assume many different values of the course of the execution of a program, just as a hardware memory cell may contain many different values. Thus, the assignment statement is a very important and frequently used statement. © Examples of imperative languages: • FORTRAN, Algol, COBOL, Pascal, C (and to some extent C++), BASIC, Ada - and many more. © PL/I • PL/I (1963-5): was one of the few languages that attempted to be a general purpose language, rather than aiming at a particular category of programming. • PL/I incorporated a blend of features from FORTRAN, ALGOL, and COBOL, plus allowed programmers to create concurrent tasks, handle run-time exceptions, use recursive procedures, and use pointers.