Function in C

Function

A block of code written to perform a specific task is called a function. Function in C programming is a reusable block of code that makes a program easier to understand, test and can be easily modified without changing the calling function. Functions divide the code and modularize the program for better and effective results. In short, a larger program is divided into various subprograms, which are called functions.

Advantages of using function

• Increase code reusability
• Program development is faster
• Debugging will be easier
• Reduces complexity

Types of functions

1. Library function

It is a predefined function in a header file. The programmer can use this function by simply adding a header file to the program. One cannot change or alter the meaning of this function. Examples:

- printf(), scanf()
- getch(), clrscr()
- pow(), sqrt()

2. User-Defined Function

A user-defined function is declared, defined, and used by the programmers according to their requirements. There are 4 different types of user-defined functions:
- Function with arguments and a return value
- Function with arguments and no return value
- Function with no arguments and a return value
- Function with no arguments and no return value

Difference Between:

Components of Function

1. Function declaration (prototype)

Declaration of function informs the compiler about the existence of function and it will be defined and used later.

return_type function_name(parameter-list);

2. Function definition

A user-defined function must be defined before it is called or used in the program. It consists of all the code required for its implementation.

return-value-type function-name(parameter-list)  
{declarations and statements}

3. Function call

After declaring and defining user-defined function, it can be used when needed. Generally, a user-defined function is used by calling it by passing required data.

function_name(argument-list);

4. Return statement

One of the main features of the function is that it can return a value to the calling function. In order for a function to return a value to the calling function, the function should have a return statement.

Accessing a Function by passing values

Function with both arguments and a return value.

This type of function has two-way communication.

#include<stdio.h>  
#include<conio.h>  
int rect_area(int,int);  
void main()  
{  
  int l, b, a;  
  print("Enter the length and breadth: n");  
  scanf("%d %d", &l, &b);  
  a= rect_area(l,b);  
  printf("The area of rectangle is %d", a);  
  getch();  
}  
int rect_area(int l, int b)  
{  
  int area;  
  area= l*b;  
  return area;  
}  

Output
Enter the length and breadth:
5
7
The area of rectangle is 35

Function with arguments but no return type

This type of function has one-way communication

#include<stdio.h>  
#include<conio.h>  
void rect_area(int,int);  
void main()  
{  
  int l, b;  
  printf("Enter the length and breadth: n");  
  scanf("%d %d", &l, &b);  
  rect_area(l,b);  
  getch();  
}  
void rect_area(int l, int b)  
{  
  int area;  
  area= l*b;  
  printf("The area of rectangle is %d",area);  
}  

Output
Enter the length and breadth:
5
7
The area of rectangle is 35

Function without arguments but with return type.

Here, an arguement is not passed from the calling function, but there is a need for a return statement.

#include<stdio.h>  
#include<conio.h>  
int rect_area(void);  
void main()  
{  
  int a;  
  a= rect_area();  
  printf("The area of rectangle is %d", a);  
  getch();  
}  
int rect_area(void)  
{  
  int area,l,b;  
  printf("Enter the length and breadth: \n");  
  scanf("%d,%d", &l, &b);  
  area= l*b;  
  return(area);  
}  

Output
Enter the length and breadth:
5
7
The area of rectangle is 35

Function without any arguments and return type.

If we do not want a return value, we must use the type void and miss out on the return statement.

#include<stdio.h>  
#include<conio.h>  
void rect_area();  
void main()  
{  
  rect_area();  
  getch();  
}  
void rect_area()  
{  
  int l,b, area;  
  printf("Enter length and breadth: \n");  
  scanf("%d,%d", &l, &b);  
  area=l*b;  
  printf("The area of rectangle is %d",area);  
}  

Output:
Enter the length and breadth:
5
7
The area of rectangle is 35