C Program to Reverse a Number

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, 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.