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C++ Program to Swap Two Numbers

C++ Program to Swap Two Numbers

This example contains two different techniques to swap numbers in C programming. The first program uses temporary variable to swap numbers, whereas the second program doesn't use temporary variables.

Example 1: Swap Numbers (Using Temporary Variable)

#include <iostream>
using namespace std;

int main()
{
    int a = 5, b = 10, temp;

    cout << "Before swapping." << endl;
    cout << "a = " << a << ", b = " << b << endl;

    temp = a;
    a = b;
    b = temp;

    cout << "\nAfter swapping." << endl;
    cout << "a = " << a << ", b = " << b << endl;

    return 0;
}

Output

Before swapping.
a = 5, b = 10

After swapping.
a = 10, b = 5

To perform swapping in above example, three variables are used.

The contents of the first variable is copied into the temp variable. Then, the contents of second variable is copied to the first variable.

Finally, the contents of the temp variable is copied back to the second variable which completes the swapping process.

You can also perform swapping using only two variables as below.


Example 2: Swap Numbers Without Using Temporary Variables

#include <iostream>
using namespace std;

int main()
{
    
    int a = 5, b = 10;

    cout << "Before swapping." << endl;
    cout << "a = " << a << ", b = " << b << endl;

    a = a + b;
    b = a - b;
    a = a - b;

    cout << "\nAfter swapping." << endl;
    cout << "a = " << a << ", b = " << b << endl;

    return 0;
}

The output of this program is the same as the first program above.

Let us see how this program works:

  1. Initially, a = 5 and b = 10.
  2. Then, we add a and b and store it in a with the code a = a + b. This means a = 5 + 10. So, a = 15 now.
  3. Then we use the code b = a - b. This means b = 15 - 10. So, b = 5 now.
  4. Again, we use the code a = a - b. This means a = 15 - 5. So finally, a = 10.

Hence, the numbers have been swapped.

Note: We can use multiplication and division instead of addition and subtraction. However, this won't work if one of the numbers is 0.

int a = 5, b = 10;

// using multiplication and division for swapping
a = a * b;    // a = 50
b = a / b;    // b = 5
a = a / b;    // a = 10