What is function in c.

C functions are basic building blocks in a program. All C programs are written using functions to improve re-usability, understandability and to keep track on them.

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.

Defining a Function:

The general form of a function definition in C programming language is as follows:

return_type function_name( parameter list )

{

   body of the function

}

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;

}

Function Declarations:

A function declaration tells the compiler about a function name and how to call the function. The actual body of the function can be defined separately.

A function declaration has the following parts:

return_type function_name( parameter list );

For the above defined function max(), following is the function declaration:

int max(int num1, int num2);

Parameter names are not important in function declaration only their type is required, so following is also valid declaration:

int max(int, int);

Function declaration is required when you define a function in one source file and you call that function in another file. In such case you should declare the function at the top of the file calling the function.

Calling a Function:

While creating a C function, you give a definition of what the function has to do. To use a function, you will have to call that function to perform the defined task.

When a program calls a function, program control is transferred to the called function. A called function performs defined task and when its return statement is executed or when its function-ending closing brace is reached, it returns program control back to the main program.

To call a function, you simply need to pass the required parameters along with function name, and if function returns a value, then you can store returned value. For example:

#include <stdio.h>

#include<conio.h>

/* function declaration */

int max(int num1, int num2);

int main ()

{

   /* local variable definition */

   clrscr();

   int a = 100;

   int b = 200;

   int ret;

   /* calling a function to get max value */

   ret = max(a, b);

   printf( "Max value is : %d\n", ret );

getch();

}

/* 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;

}

I kept max() function along with main() function and compiled the source code. While running final executable, it would produce the following result:

Max value is : 200