4 Ways to Swap Numbers in C++

First Way – Using a built-in swap function

C++ Standard Template Library has a built-in function (std::swap) that you may use to swap two numbers.

You simply provide two numbers to swap() function i.e.

In this way, you do not need a third variable.

An example of using the C++ swap function

The example below shows using the swap() function to interchange two variable values by using swap() function:

#include <bits/stdc++.h>

using namespace std;

int main() {

   int x = 35, y = 75;

   cout << "Value of x before swap: " <<x << "\n";

   cout << "Value of y before swap: " <<y << "\n";

   //Using swap() function swap two values

   swap(x, y);

   cout << "####################################\n";

   cout << "Value of x after swap: " <<x << "\n";

   cout << "Value of y after swap: " <<y << "\n";

   return 0;

}

Output:

Taking user input for swapping two numbers program

#include <bits/stdc++.h>
using namespace std;
int main() {
int x,y;
cout << "Enter first number: ";
cin >> x;
cout << "Enter second number: ";
cin >> y;
cout << "####################################\n";

cout << "Value of x before swap: " <<x << "\n";
cout << "Value of y before swap: " <<y << "\n";
//Using swap() function swap two values
swap(x, y);
cout << "####################################\n";
cout << "Value of x after swap: " <<x << "\n";
cout << "Value of y after swap: " <<y << "\n";
return 0;
}

A sample output:

Second way: Using a temporary third variable technique to swap numbers

As the target is to swap two variable values.

• We can use the third variable to temporarily hold the first variable value.
• Then copy the contents of the second variable to the first.
• Finally, copy the contents of the third variable (temporary) to the second variable.

See this in action below:

#include <iostream>

using namespace std;

int main()

{

   int x,y,z;

    cout << "Enter first number: ";

    cin >> x;

    cout << "Enter second number: ";

    cin >> y;

   cout << "####################################\n";

    cout << "Numbers Before swapping" << endl;
    cout << "x = " << x << "\n y = " << y << endl;

    z = x;
    x = y;
    y = z;

    cout << "\nNumbers After swapping" << endl;
    cout << "x = " << x << "\n y = " << y << endl;

    return 0;

}

Sample Output:

In the program,

• The user is asked to two numbers to swap
• Numbers are assigned to variables x and y
• A temporary variable z is used to hold the value of x

Swap numbers without a third variable by + and –

In this technique, we will perform addition and subtraction to swap the numbers of two variables.

Suppose:

Done?

Let us see this in C++ program:

#include <iostream>

using namespace std;
int main()

{

   int x,y;

    cout << "Enter first number: ";
    cin >> x;
    cout << "Enter second number: ";
    cin >> y;
    cout << "####################################\n";

        cout<<"Numbers Before swap\n x= "<<x<<"\n y= "<<y<<endl;

        x=x+y;
        y=x-y;
        x=x-y;

        cout << "####################################\n";

        cout<<"Numbers After swap\n x= "<<x<<"\n y= "<<y<<endl;

    return 0;
}

A sample output:

Using * and / for number swapping example

You may also use division and multiplication to swap numbers without using the built-in swap function or a third temporary variable.

Again, let us suppose:

x = 10

y = 20

The logic to achieve the result is:

Swapped?

C++ program to swap by /* technique

#include <iostream>

using namespace std;

int main()

{

   int x,y;

    cout << "Enter first number: ";

    cin >> x;

    cout << "Enter second number: ";

    cin >> y;

    cout << "####################################\n";

        cout<<"Numbers Before swap\n x= "<<x<<"\n y= "<<y<<endl;

            x=x*y;
            y=x/y;
            x=x/y;

        cout << "####################################\n";
        cout<<"Numbers After swap\n x= "<<x<<"\n y= "<<y<<endl;

    return 0;

}

Sample output as we entered two numbers: