C Program to Swap Two Numbers (Using Third Variable / Without Third Variable)

Swapping means exchanging the values of two variables. This program demonstrates two methods to swap numbers — one using a temporary variable and another without using any third variable.

Concept Overview

In the first approach, a temporary variable is used to store one of the numbers temporarily. In the second method, arithmetic operations are used to swap values without a third variable.

Program 1: Using Third Variable

#include <stdio.h>

int main() {
    int a, b, temp;

    printf("Enter two numbers: ");
    scanf("%d %d", &a, &b);

    printf("Before Swapping: a = %d, b = %d\n", a, b);

    // Swap using a temporary variable
    temp = a;
    a = b;
    b = temp;

    printf("After Swapping:  a = %d, b = %d\n", a, b);

    return 0;
}

Sample Output (Using Third Variable)

Enter two numbers: 10 20
Before Swapping: a = 10, b = 20
After Swapping:  a = 20, b = 10

Program 2: Without Using Third Variable

#include <stdio.h>

int main() {
    int a, b;

    printf("Enter two numbers: ");
    scanf("%d %d", &a, &b);

    printf("Before Swapping: a = %d, b = %d\n", a, b);

    // Swap without using a temporary variable
    a = a + b;
    b = a - b;
    a = a - b;

    printf("After Swapping:  a = %d, b = %d\n", a, b);

    return 0;
}

Sample Output (Without Third Variable)

Enter two numbers: 15 30
Before Swapping: a = 15, b = 30
After Swapping:  a = 30, b = 15

Explanation

• Using Third Variable – A temporary variable stores one value while swapping.
• Without Third Variable – Swapping is done using arithmetic operations (`+` and `-`) or XOR logic.
• `printf()` – Displays values before and after swapping.