Swap two numbers without using a third variable | 5 methods

Given two integers, swap them without using any third variable.

Method 1: Using addition and subtraction operator

#include <iostream>

using namespace std;

// Swap using references in C++

void swap(int &x, int &y)

{

// return if both variables' data is the same, as we can't check for the

// address of a reference

if (x == y) {

return;

}

x = x + y; // Note: overflow might happen

y = x - y;

x = x - y;

}

int main()

{

int x = 3, y = 4;

swap(x, y);

cout << x << " " << y;

return 0;

}

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Note that a copy of the actual parameter address is passed in a pass by reference, and any changes made to these variables in the function will affect the original. This can also be achieved using pointers in C, as demonstrated below.

#include <stdio.h>

// Swap using pointers to a function

void swap(int *x, int *y)

{

if (*x == *y) { // Check if the two addresses are the same

return;

}

*x = *x + *y; // overflow might happen

*y = *x - *y;

*x = *x - *y;

}

int main()

{

int x = 3, y = 4;

swap(&x, &y);

printf("%d %d", x, y);

return 0;

}

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Method 2: Using multiplication and division operator

#include <iostream>

using namespace std;

void swap(int &x, int &y)

{

if (y && x != y)

{

x = x * y; // overflow can happen

y = x / y;

x = x / y;

}

int main()

{

int x = 3, y = 4;

swap(x, y);

cout << x << " " << y;

return 0;

}

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Method 3: Using Bitwise XOR operator

#include <iostream>

using namespace std;

void swap(int &x, int &y)

{

if (x != y)

{

x = x ^ y;

y = x ^ y;

x = x ^ y;

}

// in a single line

// (x == y) || ((x ^= y), (y ^= x), (x ^= y));

}

int main()

{

int x = 3, y = 4;

swap(x, y);

cout << x << " " << y;

return 0;

}

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Method 4: Using difference between two values

#include <iostream>

using namespace std;

void swap(int &x, int &y)

{

if (x != y)

{

x = x - y;

y = y + x;

x = y - x;

}

// in a single line

// (x == y) || ((x -= y), (y += x), (x = y - x));

}

int main()

{

int x = 3, y = 4;

cout << "Before swap: x = " << x << " and y = " << y;

swap(x, y);

cout << "\nAfter swap: x = " << x << " and y = " << y;

return 0;

}

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Method 5: Using single line expressions

We can also use any of the following expressions to swap two variables in a single line:

x = x ^ y ^ (y = x);
x = x + y – (y = x);
x = (x × y) / (y = x);

The following C++ program demonstrates it:

#include <iostream>

using namespace std;

void swap(int &x, int &y)

{

// x = x ^ y ^ (y = x);

// x = x + y - (y = x);

x = (x * y) / (y = x);

}

int main()

{

int x = 3, y = 4;

swap(x, y);

cout << x << " " << y;

return 0;

}

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