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?

- The program defines a function
`reverseNumber`

that takes an integer`num`

as an argument and returns the reversed number. - The function uses a static variable
`reversedNum`

to keep track of the reversed number throughout the recursion. It is initially set to 0. - Inside the
`reverseNumber`

function, the base condition is checked. If`num`

becomes 0, the function returns 0, ending the recursion. - 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. - 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. - After the recursion ends, the final value of
`reversedNum`

is returned. - In the
`main`

function, the user is prompted to enter a positive integer. - The
`scanf`

function is used to read the input number and store it in the`number`

variable. - The
`reverseNumber`

function is called with the`number`

as an argument, and the returned value is stored in the`reversedNumber`

variable. - Finally, the reversed number is printed to the console.