Subroutine

Overview

A subroutine (function, method, procedure, sub procedure, or subprogram) is a portion of code within a larger program, which performs a specific task and can be relatively independent of the remaining code.
Subroutines are similar to functions but differ in that they do not have to return a value.
- A function may be viewed as a special instance of a subroutine
Some programming languages make very little syntactic distinction between functions and subroutines.

The components of a subroutine may include:

a body of code to be executed when the subroutine is called,
parameters that are passed to the subroutine from the point where it is called, and
a value that is returned to the point where the call occurs.

reducing the duplication of code in a program.
enabling reuse of code across multiple programs,
decomposing complex problems into simpler pieces (this improves maintainability and ease of extension),
improving readability of a program, and
hiding or regulating part of the program.