Functions in 'C' (Part 2)

Calling Function: Function can be called in two ways as follow

1) Call by Value : 

• In this method we pass actual parameters or direct values to function while calling it.
• As seen in previous article.
• Example : Consider program for multiplication of two integers using function

    #include<stdio.h>

    int main()

    {

       int a=5,b=8;

       void  swap(int a,int b)

       {

            int temp = 0;

             temp = a;

             a = b;

             b = temp;

        }

        printf("Before calling function : \n");

        printf("a=%d and b=%d",a,b);

        swap(a,b);

        printf("After calling function : \n");

        printf("a=%d and b=%d",a,b);

     return 0;

   }

Output :

Before calling function :
a=5 and b=8After calling function :
a=5 and b=8

Note : 

• When we call function by passing a,b values of a,b gets copied into n,m and function is executed. Thus called as call by value.
• Here actual variable does get affected by function since function is not changing actual variables instead it copy them into formal variables and operate on formal variables.
• Thus both printf before and after calling function will print a=5 and b=8. 

2) Call by Reference : 

• Reference is nothing but address of memory location for a variable. 
• So in this method we pass reference or address of variables to function while calling it.
• As we are passing reference function will operate on actual variables and thus they may get changed after calling function.
• Reference is indicated by &var_name. & is also known as address of operator since it returns address of variable.
• Remember that in this method function definition must contain arguments as pointer to variable. Indicated by *var_name.
• * refers to content of.
• Let's see example :

#include<stdio.h>

int main ()

{

   int a=5,b=8;

   void swap(int *a,int *b)

    {

        int temp=0;

        temp = *a;

         *a=*b;

        *b = temp;

     }

   printf("Before calling function:\n");

   printf("a=%d and b=%d",a,b);

   swap(&a,&b);

   printf("\n After calling function:\n);

   printf("a=%d and b=%d",a,b);

 return 0;

}

Output:

Before calling function:
a=5 and b=8

After calling function:
a=8 and b=5

Note : 

• Here while function execution *a,*b becomes *(&a),*(&b). 
• Let's assume that value of a that is 5 stored at address101 and values at b that is 8 is stored at address 105.
• Thus above becomes *(101),*(105) referring to actual value 5 and 8.
• After execution of function actual values will get swapped or exchanged because of reference.
• Thus before calling function output will be a=5 and b=8 whereas after calling function output will be a=8 and b=5. This is difference between two methods of calling function.