C# - Swap two numbers without using Temporary Variable


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The value of two variables can be swapped without using any temporary variables. The method involves using operators like +, *, / and bitwise.

Example: Using + operator

In the below example, the + operator is used to swap the value of two variables x and y.

using System;

namespace MyApplication { 
  class MyProgram {
    static void swap(int x, int y) {
      Console.WriteLine("Before Swap.");
      Console.WriteLine("x = " + x);
      Console.WriteLine("y = " + y);

      //Swap technique
      x = x + y;
      y = x - y;
      x = x - y;

      Console.WriteLine("After Swap.");
      Console.WriteLine("x = " + x);
      Console.WriteLine("y = " + y);
    }  

    static void Main(string[] args) {
      swap(10, 25);
    }
  }
}

Output

Before Swap.
x = 10
y = 25
After Swap.
x = 25
y = 10

Example: Using * operator

Like + operator, the * operator can also be used to swap the value of two variables x and y.

using System;

namespace MyApplication { 
  class MyProgram {
    static void swap(int x, int y) {
      Console.WriteLine("Before Swap.");
      Console.WriteLine("x = " + x);
      Console.WriteLine("y = " + y);

      //Swap technique
      x = x * y;
      y = x / y;
      x = x / y;

      Console.WriteLine("After Swap.");
      Console.WriteLine("x = " + x);
      Console.WriteLine("y = " + y);
    }  

    static void Main(string[] args) {
      swap(10, 25);
    }
  }
}

Output

Before Swap.
x = 10
y = 25
After Swap.
x = 25
y = 10

Example: Using / operator

Smilarly / operator can also be used to swap the value of two variables x and y.

using System;

namespace MyApplication { 
  class MyProgram {
    static void swap(float x, float y) {
      Console.WriteLine("Before Swap.");
      Console.WriteLine("x = " + x);
      Console.WriteLine("y = " + y);

      //Swap technique
      x = x / y;
      y = x * y;
      x = y / x;

      Console.WriteLine("After Swap.");
      Console.WriteLine("x = " + x);
      Console.WriteLine("y = " + y);
    }  

    static void Main(string[] args) {
      swap(10, 25);
    }
  }
}

Output

Before Swap.
x = 10
y = 25
After Swap.
x = 25
y = 10

Example: Using bitwise operator

The bitwise XOR (^) operator can also be used to swap the value of two variables x and y. It returns 1 when one of two bits at same position in both operands is 1, otherwise returns 0.

using System;

namespace MyApplication { 
  class MyProgram {
    static void swap(int x, int y) {
      Console.WriteLine("Before Swap.");
      Console.WriteLine("x = " + x);
      Console.WriteLine("y = " + y);

      //Swap technique
      x = x ^ y;
      y = x ^ y;
      x = x ^ y;

      Console.WriteLine("After Swap.");
      Console.WriteLine("x = " + x);
      Console.WriteLine("y = " + y);
    }  

    static void Main(string[] args) {
      swap(10, 25);
    }
  }
}

Output

Before Swap.
x = 10
y = 25
After Swap.
x = 25
y = 10

Disadvantages of using above methods

  • The multiplication and division based approaches fail if the value of one of the variable is 0.
  • The addition based approach may fail due to arithmetic overflow. If x and y are too large, operation performed on operands may result into out of range integer.


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