Subroutine

In computer science, a subroutine (function, procedure, or subprogram) is a sequence of code which performs a specific task, as part of a larger program, and is grouped as one or more statement blocks; such code is sometimes collected into software libraries. Subroutines can be "called", thus allowing programs to access the subroutine repeatedly without the subroutine's code having been written more than once. In many programming languages the word function is reserved for subroutines that return a value; however, the C programming language and its programmers view subroutines simply as functions that do not return a value.

Related terms and clarification

Different programming languages and methodologies possess notions and mechanisms related to subprograms:

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• Subroutine is practically synonymous with "subprogram." The former term may derive from the terminology of assembly languages and Fortran.
• Function and procedure often denote a subprogram that takes parameters and may or may not have a return value. Many make the distinction between "functions", that possess return values and appear in expressions, versus "procedures", that possess no return values and appear in statements . (See also Command-Query Separation.)
• Method is a special kind of subprogram used in object-oriented programming that describes some behaviour of an object.
• Closure is a subprogram together with the values of some of its variables captured from the environment in which it was created.
• Coroutine is a subprogram that returns to its caller before completing.
• Event handler, or simply "handler," is a subprogram that is called in response to an "event", such as a computer user moving the mouse or typing on the keyboard. The AppleScript scripting language simply uses the term "handler" as a synonym for subprogram.
• Threaded code makes code even more compact. It uses a small interpreter to execute subroutines that consist of lists of subroutine addresses. The lowest levels of subroutine are the only machine language.