What is a Function?

A function is a block of code that has a name and it has a property that it is reusable i.e. it can be executed from as many different points in a C Program as required.

Function groups a number of program statements into a unit and gives it a name. This unit can be invoked from other parts of a program. A computer program cannot handle all the tasks by it self. Instead its requests other program like entities – called functions in C – to get its tasks done. A function is a self contained block of statements that perform a coherent task of same kind

The name of the function is unique in a C Program and is Global. It means that a function can be accessed from any location with in a C Program. We pass information to the function called arguments specified when the function is called. And the function either returns some value to the point it was called from or returns nothing.

We can divide a long C program into small blocks which can perform a certain task. A function is a self contained block of statements that perform a coherent task of same kind.

Structure of a Function

There are two main parts of the function. The function header and the function body.

Function Header

In the first line of the above code

It has three main parts

  1. The name of the function i.e. sum
  2. The parameters of the function enclosed in parenthesis
  3. Return value type i.e. int

Function Body

What ever is written with in { } in the above example is the body of the function.

Function Prototypes

The prototype of a function provides the basic information about a function which tells the compiler that the function is used correctly or not. It contains the same information as the function header contains. The prototype of the function in the above example would be like

The only difference between the header and the prototype is the semicolon ; there must the a semicolon at the end of the prototype.