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Call by value and call by reference in c

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Call By Value

• In call by value, original value is not modified.In call by value, value being passed to the function is locally stored by the function parameter in stack memory location.
• If you change the value of function parameter, it is changed for the current function only.
• It will not change the value of variable inside the caller method such as main().

Example:

#include <stdio.h>
void swapnum( int var1, int var2 )
{
   int tempnum ;
   /*Copying var1 value into temporary variable */
   tempnum = var1 ;

   /* Copying var2 value into var1*/
   var1 = var2 ;

   /*Copying temporary variable value into var2 */
   var2 = tempnum ;

}
int main( )
{
    int num1 = 35, num2 = 45 ;
    printf("Before swapping: %d, %d", num1, num2);

    /*calling swap function*/
    swapnum(num1, num2);
    printf("\nAfter swapping: %d, %d", num1, num2);
}

Output:

Before swapping: 35, 45
After swapping: 35, 45

Call by reference

• In call by reference, original value is modified because we pass reference (address).
• Here, address of the value is passed in the function, so actual and formal arguments shares the same address space.
• Hence, value changed inside the function, is reflected inside as well as outside the function.

Example:

#include <stdio.h>
void swapnum ( int *var1, int *var2 )
{
   int tempnum ;
   tempnum = *var1 ;
   *var1 = *var2 ;
   *var2 = tempnum ;
}
int main( )
{
   int num1 = 35, num2 = 45 ;
   printf("Before swapping:");
   printf("\nnum1 value is %d", num1);
   printf("\nnum2 value is %d", num2);

   /*calling swap function*/
   swapnum( &num1, &num2 );

   printf("\nAfter swapping:");
   printf("\nnum1 value is %d", num1);
   printf("\nnum2 value is %d", num2);
   return 0;
}

Output:

Before swapping:
num1 value is 35
num2 value is 45
After swapping:
num1 value is 45
num2 value is 35
 

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