C Program to Reverse a Number

 you will learn to reverse the number entered by the user.

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

• C Programming Operators
• C while and do...while Loop

Reverse an Integer

#include <stdio.h>

int main() {

  int n, reverse = 0, remainder;

  printf("Enter an integer: ");
  scanf("%d", &n);

  while (n != 0) {
    remainder = n % 10;
    reverse = reverse * 10 + remainder;
    n /= 10;
  }

  printf("Reversed number = %d", reverse);

  return 0;
}

Output

Enter an integer: 2345
Reversed number = 5432

This program takes integer input from the user. Then the while loop is used until n != 0 is false (0).

In each iteration of the loop, the remainder when n is divided by 10 is calculated and the value of n is reduced by 10 times.

Inside the loop, the reversed number is computed using:

reverse = reverse * 10 + remainder;

Let us see how the while loop works when n = 2345.

n	n != 0	remainder	reverse
2345	true	5	0 * 10 + 5 = 5
234	true	4	5 * 10 + 4 = 54
23	true	3	54 * 10 + 3 = 543
2	true	2	543 * 10 + 2 = 5432
0	false	-	Loop terminates.

Finally, the reverse variable (which contains the reversed number) is printed on the screen.