Reverse a number in C

Reverse a number in C.

Problem Statement: Given a number N reverse the number and print it.

Examples:

Example 1:
Input: N = 123
Output: 321
Explanation: The reverse of 123 is 321

Example 2:
Input: N = 234
Output: 432
Explanation: The reverse of 234 is 432

Disclaimer: Don’t jump directly to the solution, try it out yourself first.

The idea is to extract digits from the end of the given number and create a new number in reverse order.

How to extract digits from the end of a number?

To extract the last digit, if you divide a number by 10, then the remainder will be the last digit. We can simply use the modulo(%) operator to do this, for example the last digit of 123 will be (123 % 10), which is 3.

To reduce the number by one digit from the end, simply divide the number by 10. example: to reduce 123 to 12, simply do (123/10) which is equal to 12.

To create a number from digits: The idea is to start with 0, and for every digit, multiply the number generated so far by 10, and add the digit to it.

For example, to create a number from digits: [1,2,3]:

Consider the number, num = 0.

Then,

For first digit: 1
num = num*10 + 1 = 0*10 + 1 = 1;

For second digit: 2
num = num*10 + 2 = 1*10 + 2 = 12;

For third digit: 3
num = num*10 + 2 = 12*10 + 3 = 123;

Approach:

• Run a while loop until the given number N is equal to zero while(N!=0)
• Initialize a variable reverse = 0;
• now in each step take the remainder of the given number N and store it as a variable digit, digit = N % 10
• Also, Divide the number by 10. N= N / 10
• in each step, the variable reverse get updated as reverse = reverse*10+digit.

Code:

#include<stdio.h>

int main()
{
    int N = 123;
    int num = N;
    int reverse = 0;
    while(N!=0)
    {
        int digit = N%10;
        reverse = reverse*10+digit;
        N = N/10;
    }
    printf("The reverse of the %d is %d",num,reverse);
}

if __name__ == '__main__':
    N = 123
    num = N
    reverse = 0
    while N != 0:
        digit = N % 10
        reverse = reverse * 10 + digit
        N = N // 10
    print("The reverse of the {} is {}".format(num, reverse))

Special thanks to Subhrajit Das for contributing to this article on takeUforward. If you also wish to share your knowledge with the takeUforward fam, please check out this article