Swap Two Numbers in C

In this example, you will learn to swap two numbers in C programming using two different techniques.

To understand this example, you should have the knowledge of the following C programming topics:

• C Data Types
• C Programming Operators
• C Input Output (I/O)

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Swap Numbers Using Temporary Variable

#include<stdio.h>
int main() {
      double first, second, temp;
      printf("Enter first number: ");
      scanf("%lf", &first);
      printf("Enter second number: ");
      scanf("%lf", &second);

      // Value of first is assigned to temp
      temp = first;

      // Value of second is assigned to first
      first = second;

      // Value of temp (initial value of first) is assigned to second
      second = temp;

      printf("\nAfter swapping, firstNumber = %.2lf\n", first);
      printf("After swapping, secondNumber = %.2lf", second);
      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 temp variable is assigned the value of the first variable.

Then, the value of the first variable is assigned to the second variable.

Finally, the temp (which holds the initial value of first) is assigned to second. This completes the swapping process.

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Swap Numbers Without Using Temporary Variables

#include <stdio.h>
int main() {
    double a, b;
    printf("Enter a: ");
    scanf("%lf", &a);
    printf("Enter b: ");
    scanf("%lf", &b);

    // Swapping

    // a = (initial_a - initial_b)
    a = a - b;   
 
    // b = (initial_a - initial_b) + initial_b = initial_a
    b = a + b;

    // a = initial_a - (initial_a - initial_b) = initial_b
    a = b - a;

    printf("After swapping, a = %.2lf\n", a);
    printf("After swapping, b = %.2lf", b);
    return 0;
}

Output

Enter a: 10.25
Enter b: -12.5
After swapping, a = -12.50
After swapping, b = 10.25