Swap two numbers without a temporary variable

For no reason, I was reminded of a simple code snippet to swap (interchange) two numbers that I had discovered in my early programming days. I may have used it once or twice in my 10 years of being a professional software developer.

Swapping two numbers is a common use case when working with some algorithms and the like.

Given two variables, let’s say a and b, we can swap their values without using a temporary variable as:

b = (a + b) - (a = b);

It might be be a bit confusing at first, but works based on how the compiler does evaluations. I have tested this as a Java project and even works with negative numbers as well. I am pretty sure it would also work on C/C++ too.

public class SwapSample {

	public static void main(String[] args) {
		int a = 10, b = 20;
		printVariables("Before", a, b);
		
		b = (a + b) - (a = b);
		
		printVariables("After ", a, b);
	}

	private static void printVariables(String message, int a, int b) {
		System.out.println(message + ": a = " + a + " & b = " + b);
	}
}

The above code would produce the output as:

Before: a = 10 & b = 20 After : a = 20 & b = 10

Keep coding.