How Can You Swap Two Variables Without Using a Third Variable?

Swapping Variables Without a Third Variant

Introduction:

Swapping the values of two variables is a common programming task. Typically, a third variable is used as a temporary placeholder to facilitate the exchange. However, in some scenarios, it may be desirable to avoid creating an extra variable for memory optimization or other reasons.

Problem Statement:

Swap the values of two variables a and b without using a third variable.

Solution: XOR Swap Algorithm

The XOR swap algorithm leverages the XOR operator (^) to swap the contents of two variables. The algorithm is defined as:

void xorSwap(int* x, int* y) {
    if (x != y) { //ensure that memory locations are different
       *x ^= *y;
       *y ^= *x;
       *x ^= *y;
    }
}

Implementation Details:

• The if statement checks if x and y have different memory locations to ensure they are not pointing to the same value.
• The XOR operator is applied three times to consecutively swap the values. Each XOR operation flips the bits of the corresponding variable, effectively exchanging their contents.

Example:

Let's demonstrate the algorithm with a = 10 and b = 15:

// Before swap
a = 10 (00001010)
b = 15 (00001111)

// XOR step 1
a = a ^ b = 00001010 ^ 00001111 = 00000101

// XOR step 2
b = b ^ a = 00001111 ^ 00000101 = 00001010

// XOR step 3
a = a ^ b = 00000101 ^ 00001010 = 00001111

// After swap
a = 15
b = 10

Considerations:

While the XOR swap algorithm can be efficient, it's generally not recommended for use in typical programming scenarios. Modern compilers can optimize the use of a temporary variable, making it more efficient to swap values in most cases.

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