A function is
a group of statements that together perform a task. Every C program has at
least one function which is main(), and
all the most trivial programs can define additional functions.
You can divide
up your code into separate functions. How you divide up your code among
different functions is up to you, but logically the division usually is so each
function performs a specific task.
A function
declaration tells the compiler about a function's name, return type, and
parameters. A function definition provides the actual body of the function.
The C standard
library provides numerous built-in functions that your program can call. For
example, function strcat() to
concatenate two strings, function memcpy()
to copy one memory location to another location and many more functions.
A function is
known with various names like a method or a sub-routine or a procedure etc.
Defining
a Function
The general
form of a function definition in C programming language is as follows:
return_type
function_name( parameter list )
A function definition in C programming
language consists of a function header and a function body. Here are all the
parts of a function:
·
Return
Type: A function may return a value. The
return_type is the data type of the value the function returns. Some functions
perform the desired operations without returning a value. In this case, the
return_type is the keyword void.
·
Function
Name: This is the actual name of the function.
The function name and the parameter list together constitute the function
signature.
·
Parameters:
A parameter is like a placeholder. When a function is invoked, you pass a value
to the parameter. This value is referred to as actual parameter or argument.
The parameter list refers to the type, order, and number of the parameters of a
function. Parameters are optional; that is, a function may contain no
parameters.
·
Function
Body: The function body contains a collection of
statements that define what the function does.
Example:
Following is the source code for a function called max(). This function takes two parameters num1 and num2 and returns the maximum between the two:
/* function returning the max between two numbers */
int max(int num1, int num2)
{
/* local variable declaration */
int result;
if (num1 > num2)
result = num1;
else
result = num2;
return result;
}
