![]() PL/I NONASSIGNABLE parameters, Ada IN parametersĪ function call may also have side effects such as modifying data structures in a computer memory, reading from or writing to a peripheral device, creating a file, halting the program or the machine, or even delaying the program's execution for a specified time. Like call by value except that the parameter is treated as a constant Like a macro – replace the parameters with the unevaluated argument expressions, then evaluate the argument in the context of the caller every time that the called routine uses the parameter. The value computed for that argument by the function is copied back to the argument on return from the functionĪ copy of the value of the argument is passed to the function and the value computed for that argument by the function is copied back to the argument on return from the function Selectable in most Algol-like languages after Algol 60, such as Algol 68, Pascal, Delphi, Simula, CPL, PL/M, Modula, Oberon, Ada, and many others. C, C++, Java (References to objects and arrays are also passed by value)Ī reference to an argument, typically its address, is passed to the function The argument is evaluated and a copy of the value is passed to the functionĭefault in most Algol-like languages after Algol 60, such as Pascal, Delphi, Simula, CPL, PL/M, Modula, Oberon, Ada, and many others. ![]() Different programming languages may use different conventions for passing arguments: The calling program provides actual values for these parameters, called arguments. The content of a function is its body, which is the piece of program code that is executed when the function is called or invoked.Ī function may be written so that it expects to obtain one or more data values from the calling program (to replace its parameters or formal parameters). The discipline of OOP is based on objects and methods (which are functions attached to these objects or object classes). Functions, often collected into libraries, are an important mechanism for sharing and trading software. Judicious use of functions (for example, through the structured programming approach) will often substantially reduce the cost of developing and maintaining a large program, while increasing its quality and reliability. įunctions are a powerful programming tool, and the syntax of many programming languages includes support for writing and using subroutines. However, Alan Turing had discussed subroutines in a paper of 1945 on design proposals for the NPL ACE, going so far as to invent the concept of a return address stack. Maurice Wilkes, David Wheeler, and Stanley Gill are generally credited with the formal invention of this concept, which they termed a closed sub-routine, contrasted with an open subroutine or macro. The idea of a subroutine was initially conceived by John Mauchly and Kathleen Antonelli during their work on ENIAC, and recorded in a January 1947 Harvard symposium on "Preparation of Problems for EDVAC-type Machines". Ī function is often coded so that it can be started several times and from several places during one execution of the program, including from other functions, and then branch back ( return) to the next instruction after the call, once the function's task is done. The generic umbrella term callable unit is sometimes used. Technically, these terms all have different definitions, and the nomenclature varies from language to language. In different programming languages, a function may be called a routine, subprogram, subroutine, or procedure in object-oriented programming (OOP), it may be called a method. This unit can then be used in programs wherever that particular task should be performed.įunctions may be defined within programs, or separately in libraries that can be used by many programs. In computer programming, a function or subroutine is a sequence of program instructions that performs a specific task, packaged as a unit. JSTOR ( February 2013) ( Learn how and when to remove this template message).Unsourced material may be challenged and removed.įind sources: "Function" computer programming – news ![]() Please help improve this article by adding citations to reliable sources. This article needs additional citations for verification.
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