C Program To Reverse a Number

Write a program to reverse a number or digits in C, a very basic and commonly asked question in interviews and exams. Today you will learn the standard method to reverse the number or digits and later we will tell you the error or bug which ever reverse number program have and how to remove that error completely!

Also Read: C Program for Palindrome

Source Code:

#include <stdio.h>
#include <conio.h>

void main(){
    int num , rev=0;
    printf("--- Reverse Number Program In C ---\n\n");
    printf("Enter a Number: ");
    scanf("%d",&num);
    while(num>0){
        rev = rev*10 + num%10;
        num = num / 10;
    }
    printf("Reverse is %d",rev);
    getch();
}

Output:

ERROR / BUG:
The above program work perfectly but when you enter a number having 0 (zero)s at the end than you will find out what's wrong with this program! ( See above output image carefully )
e.g If you enter 540 than the reversed number will be 45 instead of 045.

Correction:
So the only thing we have to do is count the leading number of zeros and print them before the reversed number. Lets see how to do that!

Correct Source Code:

#include <stdio.h>
#include <conio.h>

void main(){
    int num , temp, rev=0, c=0, i=0;
    printf("--- Reverse Number Program In C ---\n\n");
    printf("Enter a Number: ");
    scanf("%d",&num);
    temp = num;
    while(num>0){
        rev = rev*10 + num%10;
        //Check for zeros
        if(num%10==0 && i==0) c++;
        else i=1;
        num = num / 10;
    }
    printf("Reverse is ");
    for(i=0;i<c;i++){
      printf("0");
    }
    printf("%d",rev);
    getch();
}

Output: