C Program to Reverse a Number

Reverse an Integer

#include <stdio.h>

int main() {
  int n, reverse = 0, remainder, original;

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

  original = n;  

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

  if (original % 10 == 0) {
    printf("Reversed number = %d", reverse);
    
    while (original % 10 == 0) {
      printf("0");
      original /= 10;
    }
  } else {
    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.

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