Call by Value

C Categories

« Previous Point - Passing & Returning Arguments

Definition

When we pass value of a variable as an argument from the caller function to the function definition, it is called as call by value or passing by value.

Description

Value of actual arguments are copied to the formal arguments.
Change in formal argument values doesn't affect the actual arguments ,as formal arguments are limited to the specific function body.

swap(a,b); //caller function with actual arguments
.
.
.
swap(int x, int y) //function definition with formal arguments
{
//function body
}

When to use

When function does not need to alter the values of the original variables in the calling function or program.

Source code

#include <conio.h>
#include <stdio.h>
void main()
{
int a=1,b=2;
clrscr();
printf("\nOriginal values of a:%d, b:%d",a,b);
swap(a,b);
printf("\nAfter swaping the values of a:%d, b:%d",a,b);
getch();
}
swap(int x, int y)
{
int temp = x;
x=y;
y=temp;
printf("\nSwaped values in swap function a:%d, b:%d",x,y);
return 0;
}

Output

Original values of a:1, b:2
Swaped values in swap function a:2, b:1
After swaping the values of a:1, b:2

Program working steps

First 2 lines are preprocessor directives which include defintion of functions like clrscr(), printf() etc.
Void main function, from where the program execution starts.
Declaration of two variables a and b with integer data-type.
clrscr() fucntion to clear the screen like cls in windows and clear in linux.
Printing of original values a and b before swapping.
swap(a,b); caller function with two arguments a,b calls swap function written on line no.13.
So program control moves to line no.13 where values of a and b are copied into the declared variable x and y.
Variable temp is used for temporary storage to swap the values of x and y.
Swaped values in swap function of a and b are then printed and program control is transfered back to main function using return 0; statement.
After returning back to main function next line no.10 is executed printing the value of a and after swap.
getch() function to wait for user to exit from the program.
From output of the program you can analyze that the value changed in the swap function doesn't affects the value in the main function.

« Previous Point - Passing & Returning Arguments

Next Point - Call by Reference »

Tip Box

Remember

Variable name of actual and formal arguments should not be same.