Swapping the value of a and b without using a temporary variable.

The most obvious way to perform a swap is to use a temporary C variable; however, there are also some unique methods to swap values without using any extra memory. In this article, we will see two different and efficient ways to swap without a temporary variable.

1)Starting with XOR
XOR (Exclusive OR) is a bitwise operator that operates on the binary forms of numbers. The XOR operator compares each corresponding bit of two numbers and returns 1 if the bits are different and 0 if they are the same.

XOR Table:

Some Useful Properties:

• A ^ A = 0

• A ^ 0 = A

• A ^ B ^ B = A

Code to Swap Variables Using XOR

#include <stdio.h>

int main() {
    int a, b;

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

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

    // Swap using XOR
    a = a ^ b;  // Step 1: a holds the XOR of a and b
    b = a ^ b;  // Step 2: b now holds the original value of a
    a = a ^ b;  // Step 3: a now holds the original value of b

    // Display swapped values
    printf("After swapping: a = %d, b = %d\n", a, b);

    return 0;
}

Explanation of XOR Logic:
Let’s assume:

• a = 2 (binary: 0010)

• b = 3 (binary: 0011)

  Step 1: a = a ^ b

a = 2 ^ 3 = 0010 ^ 0011 = 0001  (a now holds 1)

Step 2: b = a ^ b

b = 1 ^ 3 = 0001 ^ 0011 = 0010  (b now holds 2, the original value of a)

Step 3: a = a ^ b

a =  1 ^ 2 = 0001 ^ 0010 = 0101  (a now holds 3, the original value of b)

Output:

Enter two integers:
2 3
Before swapping: a = 2, b = 3
After swapping: a = 3, b = 2

Second Method: Swapping Using Arithmetic Operations.

Arithmetic operations can also be used to swap two variables without the need for a temporary variable.

#include <stdio.h>

int main() {
    int a, b;


    printf("Enter two integers:\n");
    scanf("%d %d", &a, &b);



    // Swap using arithmetic operations
    a = a + b;  // Step 1: a holds the sum of a and b
    b = a - b;  // Step 2: b now holds the original value of a
    a = a - b;  // Step 3: a now holds the original value of b

    // Display swapped values
    printf("After swapping: a = %d, b = %d\n", a, b);

    return 0;
}

Output:

Enter two integers:
2 3
Before swapping: a = 2, b = 3
After swapping: a = 3, b = 3

Conclusion:

1. XOR Swap Method:

   • Pros:

     • No overflow issues (works with any integer size).

     • Good use of bitwise operations.

   • Cons:

     • lil bit confusing to beginners.

     • Doesn't work if the variables refer to the same memory location (e.g., a = b).

2. Arithmetic Swap Method:

   • Pros:

     • Simple and easy to understand.

   • Cons:

     • Might cause an overflow if the sum of a and b exceeds the range of the integer type.