How to Switch the Values of Two Variables Without Using a Temporary Variable

In programming, there are many times that you need to switch two variable values (such as in a Bubble Sort). Most people would show you how to do it with three variables and use wasteful operations, but I can show you how to do it with two...EFFICIENTLY!

Difficulty: Easy

Instructions

Things You'll Need:

• A basic understanding of binary numbers
• To know how XOR works

1. 
    

   Understanding XOR:
   
   XOR or Exclusive-Or, is similar to the commonly used INCLUSIVE-Or, except that if both inputs are 1, the output is 0 (as opposed to INCLUSIVE-Or where the value is 1).
   
   
   This addresses this case where we normally do something like:
   
   int ii1 = 1;
   int ii2 = 2;
   int tmp;
   
   tmp = ii1;
   ii1 = ii2;
   ii2 = tmp;

2. Now, the magic:
   
   A triple XOR performed on two variables will SWITCH THEM!!!
   
   So, in C#:
   
   int ii1 = 1;
   int ii2 = 2;
   
   ii1 ^= ii2;
   ii2 ^= ii1;
   ii1 ^= ii2;
   
   
   The variables have now been swapped without using a temporary variable!

Tips & Warnings

• Binary operations are usually VERY efficient.
• Be sure to perform your xor operations in the correct order.
• The ^ (circumflex or caret) is commonly the XOR operation, but check to make sure what it is in the programming language that you use (^ in C++, C#, Java and PHP, xor in Pascal, Xor in VB.NET, etc)

[pixiemama]

on 10/9/2008 5*

[raystarck]

on 6/24/2008 Nice article! keep posting

[MARCUS]

on 11/13/2007 THIS ARTICLE IS AMAZING!!!!