C Programming Tutorial

Computer Tutorial

Introduction & History of C Constants & there Types Variables & there Types C Keywords Data Type in C C - Operators First Program in C

Decision Control Statements The if statement Multiple if statement The if-else statement Ternary operator ( ? ) goto statement switch statement

Loops in C The While loop The do-while loop The for loop Nesting of Loops Break & Continue Statement

Array in C Declaration of an Array Entering Data into an Array Reading Data from an Array Array Elements in Memory Passing Array Elements to a Function Passing an Entire Array to a Function Two-Dimensional Arrays Initialising a 2-D Array Reading Data from 2-D Array Memory Map of 2-D Array Three-Dimensional Array

Pointer in C Pointer Variables Declaration Pointer Operators

String in C Pointers and Strings String Functions strlen( ) Function strcpy( ) Function strcat( ) Function strcmp( ) Function

» Function in C » Function Prototypes declaration » Call by Value » Call by Reference » Returning Values » Recursion

Structure in C Declaring a Structure Accessing Structure Members Structure Assignments Arrays of Structures Passing Structures to Functions Structure Pointers Uses of Structures

Union in C Difference Between Structure and Union

File Handling in C File Operations Opening a File Reading from a File Trouble in Opening a File Closing the File Writing to a File File Opening Modes File Handling Functions

Additional Tutorials on C

Objective Question on C

Call by Reference

Call by reference is the second way of passing arguments to a subroutine. In this method, the address of an argument is copied into the parameter. Inside the subroutine, the address is used to access the actual argument used in the call. This means that changes made to the parameter affect the argument.
C uses call by value for passing parameters, you can create a call by reference by passing a pointer to an argument, instead of passing the argument itself. Since the address of the argument is passed to the function, code within the function can change the value of the argument outside the function.
Pointers are passed to functions just like any other argument. Of course, you need to declare the parameters as pointer types.

A Program to demonstrate call by Reference

\* C Program to demonstrate Call by Reference *\
# include < stdio.h >
int swap ( int *x, int *y) ;
int main( )
{

int i = 10, j = 20 ;
printf("i and j before swapping: %d %d \n", i, j) ;
swap( &i, &j ) ;
printf(" i and j after swapping: %d %d \n", i, j) ;
return ( 0 ) ;

}
void swap ( int *x, int *y)
{

int temp ;
temp = *x ;
*x = *y ;
*y = temp ;

}

Output :

i and j before swapping: 10 20
i and j after swapping: 20 10
The swap( ) function is able to exchange the values of the two variables pointed to by x and y because their addresses (not their values) are passed. Within the function, the contents of the variables are accessed using standard pointer operations, and their values are swapped.
This program manages to exchange the values of a and b using their addresses stored in x and y.

C Programming Tutorial

Call by Reference