C Program to Swap Two Numbers

 

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;

      // %.2lf displays number up to 2 decimal points
      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;

​​​​    ​// %.2lf displays number up to 2 decimal points
    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