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C Program: Swap Two Numbers (Without Third Variable)

Swapping two numbers means exchanging their values. Normally, this is done using a third (temporary) variable.
However, C allows us to swap values without using an extra variable by applying arithmetic operations (addition & subtraction or multiplication & division) or the bitwise XOR operator.

In this program, we demonstrate swapping without a third variable using arithmetic operations (+ and -). This method saves memory because no extra variable is needed.

C Program: Swap Two Numbers (Without Third Variable)

 
#include <stdio.h>   // Standard I/O header
 
int main() {
    int a, b;
 
    // Input from user
    printf("Enter first number (a): ");
    scanf("%d", &a);
 
    printf("Enter second number (b): ");
    scanf("%d", &b);
 
    // Display before swapping
    printf("\nBefore Swapping:\n");
    printf("a = %d, b = %d\n", a, b);
 
    // Swapping without third variable (using arithmetic operations)
    a = a + b;   // Step 1: Add both numbers and store in a
    b = a - b;   // Step 2: Subtract new b from sum → gives original a
    a = a - b;   // Step 3: Subtract new b from sum → gives original b
 
    // Display after swapping
    printf("\nAfter Swapping:\n");
    printf("a = %d, b = %d\n", a, b);
 
    return 0; // Successful termination
}
   

 

 
OUTPUT :
Enter first number (a): 5
Enter second number (b): 10

Before Swapping:
a = 5, b = 10

After Swapping:
a = 10, b = 5

Explanation :

1. Input: The program takes two integers a and b as input.
2. Before Swapping: Prints original values of a and b.
3. Swapping Logic:
   • a = a + b; → now a holds the sum of both numbers.
   • b = a - b; → subtracting b from sum gives the original a.
   • a = a - b; → subtracting new b (old a) from sum gives the original b.
4. After Swapping: Prints the swapped values of a and b.