C in a Nutshell, 2nd Edition

Chapter 7. Functions

All the instructions of a C program are contained in functions. Each function performs a certain task. A special function name is main()—the function with this name is the first one to run when the program starts. All other functions are subroutines of the main() function (or otherwise dependent procedures, such as call-back functions), and can have any names you wish.

Every function is defined exactly once. A program can declare and call a function as many times as necessary.

Function Definitions

The definition of a function consists of a function head (or the declarator), and a function block. The function head specifies the name of the function, the type of its return value, and the types and names of its parameters, if any. The statements in the function block specify what the function does. The general form of a function definition is as follows:

In the function head, name is the function’s name, while type consists of at least one type specifier, which defines the type of the function’s return value. The return type may be void or any object type except array types. Furthermore, type may include one of the function specifiers inline or _Noreturn, and/or one of the storage class specifiers extern or static.

A function cannot return a function or an array. However, you can define a function that returns a pointer to a function or a pointer to an array. ...