A function is a reusable portion of a program, sometimes called a procedure or subroutine.

Why write and use functions?

With functions, there are 2 major points of view

Using Functions

Predefined Functions

Building Functions

The builder of a function (a programmer) is responsible for the declaration (also known as prototype) and the definition.

Declaring a Function

Defining a Function

Scope of Identifiers

void functions and empty parameter lists

Functions and the compiler