C Program to Reverse a Number using Recursion

This C program uses recursion to reverse a given number. Recursion is a process in which a function calls itself as a subroutine. The reverseNumber function is called recursively to reverse the digits of the input number.

Problem Statement

Given a positive integer, we need to reverse the digits of that number using recursion.

C Program to Reverse a Number using Recursion

#include <stdio.h>

// Function to reverse a number using recursion
int reverseNumber(int num) {
    static int reversedNum = 0;
    if (num == 0) {
        return 0;
    }
    reversedNum = (reversedNum * 10) + (num % 10);
    reverseNumber(num / 10);
    return reversedNum;
}

int main() {
    int number, reversedNumber;

    printf("Enter a positive integer: ");
    scanf("%d", &number);

    reversedNumber = reverseNumber(number);

    printf("The reversed number is: %d\n", reversedNumber);

    return 0;
}

How it Works?

1. The program defines a function reverseNumber that takes an integer num as an argument and returns the reversed number.
2. The function uses a static variable reversedNum to keep track of the reversed number throughout the recursion. It is initially set to 0.
3. Inside the reverseNumber function, the base condition is checked. If num becomes 0, the function returns 0, ending the recursion.
4. If the base condition is not met, the function recursively calls itself with the updated value of num divided by 10. This helps in moving to the next digit of the input number.
5. During each recursive call, the function updates the reversedNum by multiplying it by 10 and adding the last digit of num obtained using the modulus operator.
6. After the recursion ends, the final value of reversedNum is returned.
7. In the main function, the user is prompted to enter a positive integer.
8. The scanf function is used to read the input number and store it in the number variable.
9. The reverseNumber function is called with the number as an argument, and the returned value is stored in the reversedNumber variable.
10. Finally, the reversed number is printed to the console.

Input/Output