Swap Two Numbers in C Program

This page contains two different techniques to swap numbers in C programming. The first program uses temporary variable to swap numbers, whereas second program does not use any temporary variable.

Program to Swap Numbers Using Temporary Variable

#include <stdio.h>
int main()
{
      double firstNumber, secondNumber, temporaryVariable;

      printf("Enter first number: ");
      scanf("%lf", &firstNumber);

      printf("Enter second number: ");
      scanf("%lf",&secondNumber);

      // Value of firstNumber is assigned to temporaryVariable
      temporaryVariable = firstNumber;

      // Value of secondNumber is assigned to firstNumber
      firstNumber = secondNumber;

      // Value of temporaryVariable (which contains the initial value of firstNumber) is assigned to secondNumber
      secondNumber = temporaryVariable;

      printf("\nAfter swapping, firstNumber = %.2lf\n", firstNumber);
      printf("After swapping, secondNumber = %.2lf", secondNumber);

      return 0;
}

Output

Enter first number: 1.20
Enter second number: 2.45

After swapping, firstNumber = 2.45
After swapping, secondNumber = 1.20

In the above program, the temporaryVariable is assigned the value of firstNumber. Then, the value of firstNumber is assigned to secondNumber. Finally, the temporaryVariable (which holds the initial value of firstNumber) is assigned to secondNumber which completes the swapping process.

Here, temporaryVariable is used to hold the value of firstNumber and doesn't have any other use except that. You can also write the swapping program without using temporaryVariable.

Program to Swap Number Without Using Temporary Variables

#include <stdio.h>
int main()
{
    double firstNumber, secondNumber;

    printf("Enter first number: ");
    scanf("%lf", &firstNumber);

    printf("Enter second number: ");
    scanf("%lf",&secondNumber);

    // Swapping process

    firstNumber = firstNumber - secondNumber;
    secondNumber = firstNumber + secondNumber;
    firstNumber = secondNumber - firstNumber;

    printf("\nAfter swapping, firstNumber = %.2lf\n", firstNumber);
    printf("After swapping, secondNumber = %.2lf", secondNumber);

    return 0;
}

Output

Enter first number: 10.25
Enter second number: -12.5

After swapping, firstNumber = -12.50
After swapping, secondNumber = 10.25