Functions in C

Today we are going to discuss about Functions...

So firstly we will discuss What is Functions?

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 is such that 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, strcat() to concatenate two strings, memcpy() to copy one memory location to another location, and many more functions.

Example Program For Functions:

#include<stdio.h>

int max(int x,int y)

{

              if(x>y)

              return x;

              else

              return y;

}

int main()

{

              int a=10;

              int b=20;

              int c=max(a,b);

              printf("maximum is %d",c);

              return 0;

}

 

USES OF C FUNCTIONS:

• C functions are used to avoid rewriting same logic/code again and again in a program.
• There is no limit in calling C functions to make use of same functionality wherever required.
• We can call functions any number of times in a program and from any place in a program.
• A large C program can easily be tracked when it is divided into functions.
• The core concept of C functions are, re-usability, dividing a big task into small pieces to achieve the functionality and to improve understandability of very large C programs.

Example Program For Parameters in functions:-

#include<stdio.h>

//parameters in funcitons

int fun(int x)

{

              x=20;

}

int main()

{

              int x=20;

              fun(x);

              printf("x =%d",x);

              return 0;

}

C FUNCTION DECLARATION, FUNCTION CALL AND FUNCTION DEFINITION:

There are 3 aspects in each C function. They are,

• Function declaration or prototype – This informs compiler about the function name, function parameters and return value’s data type.
• Function call – This calls the actual function
• Function definition – This contains all the statements to be executed.

C Function

FUNCTION CALLING:

There are two methods of calling a function, they are-

1. Call by Value

2. Call by Reference

1. CALL BY VALUE:

• In call by value method, the value of the variable is passed to the function as parameter.
• The value of the actual parameter can not be modified by formal parameter.
• Different Memory is allocated for both actual and formal parameters. Because, value of actual parameter is copied to formal parameter.

Note:

• Actual parameter – This is the argument which is used in function call.
• Formal parameter – This is the argument which is used in function definition.

Program For Call By Value:

// C program to illustrate

// call by value

#include <stdio.h>

 

// Function Prototype

void swapx(int x, int y);

 

// Main function

int main()

{

              int a = 10, b = 20;

 

              // Pass by Values

              swapx(a, b);

 

              printf("a=%d b=%d\n", a, b);

 

              return 0;

}

 

// Swap functions that swaps

// two values

void swapx(int x, int y)

{

              int t;

 

              t = x;

              x = y;

              y = t;

 

              printf("x=%d y=%d\n", x, y);

} 

2. CALL BY REFERENCE:

• In call by reference method, the address of the variable is passed to the function as parameter.
• The value of the actual parameter can be modified by formal parameter.
• Same memory is used for both actual and formal parameters since only address is used by both parameters.

Program For Call by Reference:-

// C program to illustrate

// Call by Reference

#include <stdio.h>

 

// Function Prototype

void swapx(int*, int*);

 

// Main function

int main()

{

              int a = 10, b = 20;

 

              // Pass reference

              swapx(&a, &b);

 

              printf("a=%d b=%d\n", a, b);

 

              return 0;

}

 

// Function to swap two variables

// by references

void swapx(int* x, int* y)

{

              int t;

 

              t = *x;

              *x = *y;

              *y = t;

 

              printf("x=%d y=%d\n", *x, *y);

}