Examine individual changes

'{{refimprove|date=October 2011}} {{Programming paradigms}} In [[computer science]], '''imperative programming''' is a [[programming paradigm]] that uses [[Statement (computer science)|statement]]s that change a program's [[state (computer science)|state]]. In much the same way that the [[imperative mood]] in [[natural language]]s expresses commands, an imperative program consists of [[command (computing)|command]]s for the [[computer]] to perform. Imperative programming focuses on describing ''how'' a program operates. The term is often used in contrast to [[declarative programming]], which focuses on ''what'' the program should accomplish without specifying ''how'' the program should achieve the result. ==Imperative and procedural programming== [[Procedural programming]] is a type of imperative programming in which the program is built from one or more procedures (also known as [[subroutine]]s or functions). The terms are often used as synonyms, but the use of procedures has a dramatic effect on how imperative programs appear and how they are constructed. Heavily-procedural programming, in which [[State (computer science)|state change]]s are localized to procedures or restricted to explicit arguments and returns from procedures, is known as [[structured programming]]. From the 1960s onwards, structured programming and [[modular programming]] in general have been promoted as techniques to improve the [[maintainability]] and overall quality of imperative programs. [[Object-oriented programming]] extends this approach.<ref>{{cite web | url = http://cs.anu.edu.au/ | title = Programming paradigms and an overview of C - COMP3610 - Principles of Programming Languages: Object-Oriented programming | author = Michael Stevens | year = 2011 | page = 5 | publisher = Australian National University | archiveurl = http://cs.anu.edu.au/student/comp3610/lectures/Paradigms.pdf | archivedate= 2011 | quote = Object oriented programming extends the concept of modularity by introducing objects | accessdate = 2012-05-22 }}</ref><!-- this does not follow at all? --> Procedural programming could be considered a step towards declarative programming. A programmer can often tell, simply by looking at the names, arguments and return types of procedures (and related comments), what a particular procedure is supposed to do, without necessarily looking at the details of how it achieves its result. At the same time, a complete program is still imperative since it 'fixes' the statements to be executed and their order of execution to a large extent. ==Declarative programming== [[Declarative programming]] contrasts with imperative and procedural programming. Declarative programming is a non-imperative style of programming in which programs describe their desired results without explicitly listing commands or steps that must be performed. ==Rationale and foundations of imperative programming== The hardware implementation of almost all computers is imperative;<ref group=note>[[Reconfigurable computing]] is a notable exception.</ref> nearly all computer hardware is designed to execute [[machine code]], which is native to the computer, written in the imperative style. From this low-level perspective, the program state is defined by the contents of memory, and the statements are instructions in the native machine language of the computer. Higher-level imperative languages use [[variable (programming)|variable]]s and more complex statements, but still follow the same paradigm. [[Recipe]]s and process [[checklist]]s, while not [[computer program]]s, are also familiar concepts that are similar in style to imperative programming; each step is an instruction, and the physical world holds the state. Since the basic ideas of imperative programming are both conceptually familiar and directly embodied in the hardware, most computer languages are in the imperative style. [[Destructive assignment|Assignment statements]], in imperative paradigm, perform an operation on information located in memory and store the results in memory for later use. High-level imperative languages, in addition, permit the [[Evaluation (disambiguation)|evaluation]] of complex [[Expression (programming)|expressions]], which may consist of a combination of [[Arithmetic#Arithmetic operations|arithmetic operations]] and [[function (mathematics)|function]] evaluations, and the assignment of the resulting value to memory. Looping statements (such as in [[while loop]]s, [[do while loop]]s and [[for loop]]s) allow a sequence of statements to be executed multiple times. Loops can either execute the statements they contain a predefined number of times, or they can execute them repeatedly until some condition changes. [[Conditional (programming)|Conditional]] [[Branch (computer science)|branching]] statements allow a sequence of statements to be executed only if some condition is met. Otherwise, the statements are skipped and the execution sequence continues from the statement following them. Unconditional branching statements allow the execution sequence to be transferred to some other part of the program. These include the jump (called "[[goto]]" in many languages), [[switch statement|switch]] and the subprogram, or [[Subroutine|procedure]], call (which usually returns to the next statement after the call). Early in the development of [[high level language]]s, the introduction of the [[block (programming)|block]] enabled the construction of programs in which a group of statements and declarations could be treated as if they were a single statement. This, alongside the introduction of [[subroutine]]s, enabled complex structures to be expressed by hierarchical decomposition into simpler procedural structures. Many imperative programming languages (such as [[FORTRAN]], [[BASIC]] and [[C (programming language)|C]]) are [[Abstraction (computer science)|abstraction]]s of [[assembly language]].<ref>{{cite book|author=Bruce Eckel|title=Thinking in Java|url=http://books.google.com/books?id=bQVvAQAAQBAJ&pg=PA24&lpg=PA24&dq=imperative&source=bl&ots=LXUh8GZ17E&sig=u2aOh64yjWEYX_nCs9NolKmKhE4&hl=en&sa=X&ei=jLv0U6i1IMKSyAS-7oKADg&ved=0CDUQ6AEwAw#v=onepage&q=imperative&f=false|publisher=[[Pearson Education]]|year=2006|isbn=978-0-13-187248-6|page=24}}</ref> ==History of imperative and object-oriented languages== The earliest imperative languages were the machine languages of the original computers. In these languages, instructions were very simple, which made hardware implementation easier, but hindered the creation of complex programs. FORTRAN, developed by [[John Backus]] at [[International Business Machines|IBM]] starting in 1954, was the first major programming language to remove the obstacles presented by machine code in the creation of complex programs. FORTRAN was a [[compiled language]] that allowed named variables, complex expressions, subprograms, and many other features now common in imperative languages. The next two decades saw the development of a number of other major high-level imperative programming languages. In the late 1950s and 1960s, [[ALGOL]] was developed in order to allow mathematical algorithms to be more easily expressed, and even served as the [[operating system]]'s target language for some computers. [[MUMPS]] (1966) carried the imperative paradigm to a logical extreme, by not having any statements at all, relying purely on commands, even to the extent of making the IF and ELSE commands independent of each other, connected only by an intrinsic variable named $TEST. [[COBOL]] (1960) and [[BASIC]] (1964) were both attempts to make programming syntax look more like English. In the 1970s, [[Pascal programming language|Pascal]] was developed by [[Niklaus Wirth]], and [[C (programming language)|C]] was created by [[Dennis Ritchie]] while he was working at [[Bell Laboratories]]. Wirth went on to design [[Modula-2]] and [[Oberon programming language|Oberon]]. For the needs of the [[United States Department of Defense]], [[Jean Ichbiah]] and a team at [[Honeywell]] began designing [[Ada programming language|Ada]] in 1978, after a 4-year project to define the requirements for the language. The specification was first published in 1983, with revisions in 1995 and 2005/6. The 1980s, saw a rapid growth in interest in [[object-oriented programming]]. These languages were imperative in style, but added features to support [[object (computing)|objects]]. The last two decades of the 20th century saw the development of a considerable number of such programming languages. [[Smalltalk-80]], originally conceived by [[Alan Kay]] in 1969, was released in 1980, by the [[Xerox Palo Alto Research Center]]. Drawing from concepts in another object-oriented language—[[Simula]] (which is considered to be the world's first [[object-oriented programming language]], developed in the 1960s)—[[Bjarne Stroustrup]] designed [[C++]], an object-oriented language based on [[C (programming language)|C]]. [[C++]] was first implemented in 1985. In the late 1980s and 1990s, the notable imperative languages drawing on object-oriented concepts were [[Perl]], released by [[Larry Wall]] in 1987; [[Python (programming language)|Python]], released by [[Guido van Rossum]] in 1990; [[Visual Basic]] and [[Visual C++]] (which included [[Microsoft Foundation Class Library|MFC]] 2.0), released by [[Microsoft]] in 1991 and 1993 respectively; [[PHP]], released by [[Rasmus Lerdorf]] in 1994; [[Java (programming language)|Java]], first released by [[Sun Microsystems]] in 1994, and [[Ruby (programming language)|Ruby]] released in 1995, by Yukihiro "Matz" Matsumoto. [[Microsoft]]'s [[.NET platform|.NET]] (2002) is imperative at its core, as are its primary target languages, [[VB.NET]] and [[C Sharp (programming language)|C#]] that run on it (however Microsoft's [[F Sharp (programming language)|F#]] is a functional language, that also runs on it). ==See also== {{Portal|Computer science}} * [[Functional programming]] * [[Comparison of programming paradigms]] * [[Declarative programming]] (contrast) * [[Programming paradigm]]s * [[Object-oriented programming]] * [[History of programming languages]] * [[List of programming languages by category#Imperative languages|List of imperative programming languages]] * [[:Category:Procedural programming languages]] lists additional imperative programming languages ==Notes== {{Reflist|group=note}} ==References== {{Reflist}} * Pratt, Terrence W. and Marvin V. Zelkowitz. ''Programming Languages: Design and Implementation'', 3rd ed. Englewood Cliffs, N.J.: Prentice Hall, 1996. * Sebesta, Robert W. ''Concepts of Programming Languages'', 3rd ed. Reading, Mass.: Addison-Wesley Publishing Company, 1996. <!--- reduced license notice by special permission of Stan Seibert, see Talk ---> ''Originally based on the article 'Imperative programming' by Stan Seibert, from [[Nupedia]], licensed under the [[GNU Free Documentation License]].'' {{Programming language}} {{Authority control}} {{DEFAULTSORT:Imperative Programming}} <!--Categories--> [[Category:Programming paradigms]] <!--Important/meaningful is some way (or vandalism?): "SAII99"-->'