What is function? - Definition from WhatIs.com
Part of the Computing fundamentals glossary:

In information technology, the term function (pronounced FUHNK-shun ) has a number of meanings. It's taken from the Latin "functio" - to perform.

1) In its most general use, a function is what a given entity does in being what it is.

2) In C language and other programming, a function is a named procedure that performs a distinct service. The language statement that requests the function is called a function call . Programming languages usually come with a compiler and a set of "canned" functions that a programmer can specify by writing language statements. These provided functions are sometimes referred to as library routines . Some functions are self-sufficient and can return results to the requesting program without help. Other functions need to make requests of the operating system in order to perform their work.

3) In mathematics, a function is a relationship between two variables called the independent variable and the dependent variable. The dependent variable has at most one value for any specific value of the independent variable. A function is usually symbolized by a lowercase, italicized letter of the alphabet, followed by the independent variable in parentheses. For example, the expression y = f ( x ), read " y equals f of x ," means that a dependent variable y is a function of the independent variable x . Functions are often graphed, and they usually appear as lines or curves on a coordinate plane.

4) In a hardware device, a function is one complete physical movement that has a discernible consequence relative to the device's purposes. In a printer, for example, this might be a carriage return or a line feed.

This was last updated in September 2005
Posted by: Margaret Rouse

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