How to swap two numbers without using a temporary variable?

Given two variables, x and y, swap two variables without using a third variable.

Method 1 (Using Arithmetic Operators)
The idea is to get sum in one of the two given numbers. The numbers can then be swapped using the sum and subtraction from sum.

C

#include <stdio.h>
int main()
{
  int x = 10, y = 5;

  // Code to swap 'x' and 'y'
  x = x + y;  // x now becomes 15
  y = x - y;  // y becomes 10
  x = x - y;  // x becomes 5

  printf("After Swapping: x = %d, y = %d", x, y);

  return 0;
}

Java

// Program to swap two numbers  without 
// using temporary variable
import java.*;

class Geeks {

    public static void main(String a[])
    {
        int x = 10;
        int y = 5;
        x = x + y;
        y = x - y;
        x = x - y;
        System.out.println("After swaping:"
             + " x = " + x + ", y = " + y);
    }
}

// This code is contributed by Sam007

Python 3


x = 10
y = 5
 
# Code to swap 'x' and 'y'

# x now becomes 15
x = x + y  

# y becomes 10
y = x - y 

# x becomes 5
x = x - y  
print("After Swapping: x =",x ," y =", y);

# This code is contributed 
# by Sumit Sudhakar

C#

// Program to swap two numbers  without 
// using temporary variable
using System;

class GFG {
public static void Main()
    {
        int x = 10;
        int y = 5;
        Console.WriteLine("Before swap:");
        Console.WriteLine("x value: " + x);
        Console.WriteLine("y value: " + y);
        x = x + y;
        y = x - y;
        x = x - y;
        Console.WriteLine("After swap:");
        Console.WriteLine("x value: " + x);
        Console.WriteLine("y value: " + y);
    }
}

// This code is contributed by Sam007

PHP

<?php
// PHP Program to swap two 
// numbers without using 
// temporary variable
$x = 10; $y = 5;

// Code to swap 'x' and 'y'
$x = $x + $y; // x now becomes 15
$y = $x - $y; // y becomes 10
$x = $x - $y; // x becomes 5

echo "After Swapping: x = ", 
       $x, "," , "y = ", $y;

// This code is contributed by m_kit
?>

Output :

After Swapping: x = 5, y = 10

Multiplication and division can also be used for swapping.

C

#include <stdio.h>
int main()
{
  int x = 10, y = 5;

  // Code to swap 'x' and 'y'
  x = x * y;  // x now becomes 50
  y = x / y;  // y becomes 10
  x = x / y;  // x becomes 5

  printf("After Swapping: x = %d, y = %d", x, y);

  return 0;
}

Java

// Java Program to swap two numbers
// without using temporary variable
import java.io.*;

class GFG 
{
    public static void main (String[] args) 
    {
        int x = 10;
        int y = 5;

        // Code to swap 'x' and 'y'
        x = x * y; // x now becomes 50
        y = x / y; // y becomes 10
        x = x / y; // x becomes 5

        System.out.println("After swaping:" +
                                " x = " + x + 
                                ", y = " + y);
    }
}

// This code is contributed by ajit

Python3

# Python3 program to 
# swap two numbers
# without using 
# temporary variable
x = 10
y = 5

# code to swap 
# 'x' and 'y'

# x now becomes 50
x = x * y

# y becomes 10
y = x // y; 

# x becomes 5
x = x // y; 

print("After Swapping: x =", 
              x ," y =", y);

# This code is contributed 
# by @ajit

C#

// C# Program to swap two 
// numbers without using 
// temporary variable
using System;

class GFG
{
    static public void Main ()
    {
        int x = 10;
        int y = 5;

        // Code to swap 'x' and 'y'
        x = x * y; // x now becomes 50
        y = x / y; // y becomes 10
        x = x / y; // x becomes 5

        Console.WriteLine("After swaping:" +
                               " x = " + x + 
                              ", y = " + y);
    }
}

// This code is contributed by ajit.


PHP

<?php
// Driver code
    $x = 10;
    $y = 5;

// Code to swap 'x' and 'y'
    $x = $x * $y; // x now becomes 50
    $y = $x / $y; // y becomes 10
    $x = $x / $y; // x becomes 5

echo "After Swapping: x = ", $x,
                " ", "y = ", $y;

// This code is contributed by m_kit
?>

Output :



After Swapping: x = 5, y = 10

Method 2 (Using Bitwise XOR)
The bitwise XOR operator can be used to swap two variables. The XOR of two numbers x and y returns a number which has all the bits as 1 wherever bits of x and y differ. For example XOR of 10 (In Binary 1010) and 5 (In Binary 0101) is 1111 and XOR of 7 (0111) and 5 (0101) is (0010).

C

#include <stdio.h>
int main()
{
  int x = 10, y = 5;

  // Code to swap 'x' (1010) and 'y' (0101)
  x = x ^ y;  // x now becomes 15 (1111)
  y = x ^ y;  // y becomes 10 (1010)
  x = x ^ y;  // x becomes 5 (0101)

  printf("After Swapping: x = %d, y = %d", x, y);

  return 0;
}

Java

import java.*;

public class GFG {

    public static void main(String a[]){
        int x = 10;
        int y = 5;
        
        // Code to swap 'x' (1010) and 'y' (0101)
        x = x ^ y; // x now becomes 15 (1111)
        y = x ^ y; // y becomes 10 (1010)
        x = x ^ y; // x becomes 5 (0101)
        
        System.out.println("After swap: x = "
                            + x + ", y = " + y);
    }
}

// This code is contributed by Sam007.

Python3

# Python 3 code to swap using XOR

x = 10
y = 5

# Code to swap 'x' and 'y'
x = x ^ y; # x now becomes 15 (1111)
y = x ^ y; # y becomes 10 (1010)
x = x ^ y; # x becomes 5 (0101)

print ("After Swapping: x = ",x ," y =", y)

# This code is contributed by
# Sumit Sudhakar

C#

// C# program to swap using XOR
using System;

class GFG
{
    public static void Main()
    {
        int x = 10;
        int y = 5;
        
        // Code to swap 'x' (1010) 
        // and 'y' (0101)
        
        // x now becomes 15 (1111)
        x = x ^ y; 
        
        // y becomes 10 (1010)
        y = x ^ y; 
        
        // x becomes 5 (0101)
        x = x ^ y; 
        
    Console.WriteLine("After swap: x = " + 
                        x + ", y = " + y);
    }
}

// This code is contributed by ajit


PHP

<?php

// Driver Code 
$x = 10;
$y = 5;

// Code to swap 'x' (1010) 
// and 'y' (0101)

// x now becomes 15 (1111)
$x = $x ^ $y; 

// y becomes 10 (1010)
$y = $x ^ $y; 

// x becomes 5 (0101)
$x = $x ^ $y; 

echo "After Swapping: x = ", $x, 
                ",", "y = ", $y;

// This code is contributed by aj_36
?>

Output :

After Swapping: x = 5, y = 10

Problems with above methods
1) The multiplication and division based approach doesn’ work if one of the numbers is 0 as the product becomes 0 irrespective of the other number.

2) Both Arithmetic solutions may cause arithmetic overflow. If x and y are too large, addition and multiplication may go out of integer range.

3) When we use pointers to variable and make a function swap, all of the above methods fail when both pointers point to the same variable. Let’s take a look what will happen in this case if both are pointing to the same variable.

// Bitwise XOR based method
x = x ^ x; // x becomes 0
x = x ^ x; // x remains 0
x = x ^ x; // x remains 0

// Arithmetic based method
x = x + x; // x becomes 2x
x = x – x; // x becomes 0
x = x – x; // x remains 0

Let us see the following program.

C

#include <stdio.h>
void swap(int *xp, int *yp)
{
    *xp = *xp ^ *yp;
    *yp = *xp ^ *yp;
    *xp = *xp ^ *yp;
}

int main()
{
  int x = 10;
  swap(&x, &x);
  printf("After swap(&x, &x): x = %d", x);
  return 0;
}


Output :

After swap(&x, &x): x = 0

Swapping a variable with itself may needed in many standard algorithms. For example see this implementation of QuickSort where we may swap a variable with itself. The above problem can be avoided by putting a condition before the swapping.

C

#include <stdio.h>
void swap(int *xp, int *yp)
{
    if (xp == yp) // Check if the two addresses are same
      return;
    *xp = *xp + *yp;
    *yp = *xp - *yp;
    *xp = *xp - *yp;
}
int main()
{
  int x = 10;
  swap(&x, &x);
  printf("After swap(&x, &x): x = %d", x);
  return 0;
}


Output :

After swap(&x, &x): x = 10

Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above



My Personal Notes arrow_drop_up

Improved By : jit_t




Practice Tags :
Article Tags :
Please write to us at contribute@geeksforgeeks.org to report any issue with the above content.

Recommended Posts:



2 Average Difficulty : 2/5.0
Based on 83 vote(s)






User Actions