C Program To Swap Two Numbers using Pointers

Lets write a C program to swap 2 numbers using pointers and function.

When we call the function, we pass the reference or address of the variable, so this method is called “Call by Reference“.

Related Read:
Swap 2 Numbers Using a Temporary Variable: C
Function / Methods In C Programming Language
Basics of Pointers In C Programming Language

Video Tutorial: C Program To Swap Two Numbers using Pointers

Source Code: C Program To Swap Two Numbers using Pointers and Function

#include<stdio.h>

void swap(int*, int*);

int main()
{
    int a, b;

    printf("Enter values for a and b\n");
    scanf("%d%d", &a, &b);

    printf("\n\nBefore swapping: a = %d and b = %d\n", a, b);

    swap(&a, &b);

    printf("\nAfter swapping: a = %d and b = %d\n", a, b);

    return 0;
}

void swap(int *x, int *y)
{
    int temp;

    temp = *x;
    *x   = *y;
    *y   = temp;
}

Output 1:
Enter values for a and b
100
200

Before swapping: a = 100 and b = 200

After swapping: a = 200 and b = 100

Output 2:
Enter values for a and b
30
20

Before swapping: a = 30 and b = 20

After swapping: a = 20 and b = 30

Logic To Swap Two Numbers using Pointers and Function

We ask the user to enter values for variable a and b. We pass the address of variable a and b to function swap().

Inside function swap() we take a local variable temp. Since address of variable a and b are passed to swap() method, we take 2 pointer variables *x and *y. Pointer variable x holds the address of a and pointer variable y holds the address of b. Using below logic we swap the values present at address a( or x ) and b( or y ).

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

Since we are directly changing the value present at particular address, the value gets reflected throughout the program and not just inside particular function. That’s why we are able to print the result inside main function and the values of variable a and b are swapped, without getting any returned value from function swap().

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