An illustration of Calling a Function in C

When you call any function : there are two way to pass Value to it .  Today we discuss benefits of these two approaches .

CALL BY Value :   

In This Cause we just pass a copy of actual value and any change to this data in called function NOT change actual Value of The data in Caller function (which passes argument ).

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Take an example : Swapping two number   without using third variable .

1. #include <stdio.h>
3. void swap (int, int);
4. int main ()
5. {
6.         int a,b;
7.         printf("An Illustration of Call by value\n");
8.         printf("\nEnter the first number :\n");
9.         scanf("%d",&a);
10.         printf("\nEnter the second number :\n");
11.         scanf("%d",&b);
12.        
13.     printf("\nCall by Value..  \n"); 
14.                 swap(a,b); //calling function and print new value in that func;
15.    
16.     printf("\nIn main function ..");
17.         printf("\nthe first number is %d \n",a);  //printing value of a & b in main 
18.         printf("\nthe second number is %d\n",b);
19.         return 0;
20. }
21. void swap (int x, int y)
22. {
23.         x=x+y; //swapping without using third variable 
24.         y=x-y;
25.         x=x-y;
26.         printf("\nNow the first number is : %d \n",x);
27.         printf("\nNow the second number is : %d \n",y);
28. }

In this above example you can see first we call the function swap by method of call by value than than print its new values in function swap . But changing value in swap function does not alter value in main function .

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CALL BY Reference  :

In this method we pass address of variable to be passed .  since now change made in values at this address obviously alter the value in caller function (here main )

Let us discuss above case : when we call by reference ....

1. #include <stdio.h>
3. void swap (int *, int *);
4. int main ()
5. {
6.         int a,b;
7.         printf("An Illustration of Call by reference\n");
8.         printf("\nEnter the first number :\n");
9.         scanf("%d",&a);
10.         printf("\nEnter the second number :\n");
11.         scanf("%d",&b);
12.         swap (&a,&b);
13.         printf("\nCall by Reference.. \n");
14.         printf("\nNow the first number is %d \n",a);
15.         printf("\nNow the second number is %d \n",b);
17.         return 0;
18. }
19. void swap (int *x, int *y) //receive address in pointer 
20. {
21.         *x=*x+*y; //swapping without using third variable 
22.         *y=*x-*y;
23.         *x=*x-*y;
24.         printf("\nNow the first number is : %d \n",*x);
25.         printf("\nNow the second number is : %d \n",*y);
26. }

you can see output ... . actual value in main function also changed .

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Output for above two program is :

Thanks : Have a Nice Day

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