C Program to Reverse a Number

1. Introduction

Reversing a number is a frequent operation in computing. For instance, checking for palindromic numbers requires the number and its reverse to be compared. In this guide, we'll understand how to write a C program that can reverse a given number.

2. Program Overview

Our program will:

1. Ask the user to input a number.

2. Reverse the entered number.

3. Display the reversed number to the user.

3. Code Program

#include <stdio.h>  // Integrate the Standard I/O library for necessary input-output functions

int main() {  // Program initiation with the main function

    int n, reversedNumber = 0, remainder;  // Declare the original number, its reversed form, and a variable for the remainder

    // Request the user for a number
    printf("Enter an integer: ");
    scanf("%d", &n);  // Read the entered number

    while (n != 0) {
        remainder = n % 10;  // Extract the last digit
        reversedNumber = reversedNumber * 10 + remainder;  // Add the extracted digit to the reversed number
        n /= 10;  // Reduce n by one digit

    printf("Reversed Number = %d\n", reversedNumber);  // Display the reversed number

    return 0;  // Signify successful completion


Enter an integer: 12345
Reversed Number = 54321

4. Step By Step Explanation

1. #include <stdio.h>: This line includes the standard input and output library, allowing us to use input and output functions.

2. int main(): This is where our program starts.

3. Variable Declaration:

  • n: Stores the user's number.
  • reversedNumber: Will store the reverse of the number.
  • remainder: Helps in extracting the last digit from the number.

4. User Input: The program prompts the user to input a number and then captures it in n.

5. The Reversal Process:

- A while loop runs as long as n is not zero.

- Within the loop:

  • We use the modulus operation (%) to get the last digit of n and store it in the remainder.
  • We multiply the current reversedNumber by 10 and add the remainder to it. This effectively appends the last digit of n to the reverse.
  • We then divide n by 10 (using /=) to drop its last digit.

- This process continues until all digits are processed, and we obtain our reversed number.

6. Output: The program then showcases the reversed number.

The strategy utilized here highlights the importance of loop constructs and basic arithmetic operations in solving problems effectively.