EXPLAIN CALL BY VALUE AND CALL BY REFERENCE WITH EXAMPLE.

There are two ways that a C function can be called from a program. 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 cannot 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

//Example of Call by Value #include <stdio.h> #include<conio.h> void swapval(int a,int b); void main() {             int a,b;             clrscr();             a=10;             b=20;             printf(“\nValues before swap a=%d and b=%d”,a,b);             swapval(a,b);             getch(); } void swapval(int a,int b) {             int tmp;             tmp=a;             a=b;             b=tmp;             printf(“\nValues after swap a=%d and b=%d”,a,b); }

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.

//Example of Call by Reference #include <stdio.h> #include<conio.h> void swapval(int *a,int *b); void main() {             int a,b;             clrscr();             a=10;             b=20;             printf(“\nValues before swap a=%d and b=%d”,a,b);             swapval(&a,&b);             getch(); } void swapval(int *a,int *b) {             int tmp;             tmp=*a;             *a=*b;             *b=tmp;             printf(“\nValues after swap a=%d and b=%d”,*a,*b); }