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C Program to Swap Two Numbers

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:


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, first number = %.2lf\n", first);
  printf("After swapping, second number = %.2lf", second);
  return 0;
}

Output

Enter first number: 1.20
Enter second number: 2.45

After swapping, first number = 2.45
After swapping, second number = 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.


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 numbers up to 2 decimal places
  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
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