Palindrome Number in C, C++, Java & Python – Code with Explanation & Examples in Short and Simple

   

C Program

#include <stdio.h>
int revNum(int n, int rev){
    if(n==0) return rev;
    return revNum(n/10, rev*10 + n%10);
}
int main(){
    int num=121;
    if(num == revNum(num,0)) printf("Palindrome");
    else printf("Not Palindrome");
}

C Output

Input:  
num = 121  

Output:  
Palindrome

C++ Program

#include <bits/stdc++.h>
using namespace std;
int revNum(int n, int rev=0){
    if(n==0) return rev;
    return revNum(n/10, rev*10 + n%10);
}
int main(){
    int num=12321;
    cout << (num == revNum(num) ? "Palindrome" : "Not Palindrome");
}

C++ Output

Input:  
num = 12321

Output:  
Palindrome

JAVA Program

class Main{
    static int revNum(int n, int rev){
        if(n==0) return rev;
        return revNum(n/10, rev*10 + n%10);
    }
    public static void main(String[] args){
        int num=1234;
        System.out.print(num == revNum(num,0) ? "Palindrome" : "Not Palindrome");
    }
}

JAVA Output

Input:  
num = 1234 

Output:  
Not Palindrome

Python Program

def rev_num(n, rev=0):
    if n == 0:
        return rev
    return rev_num(n//10, rev*10 + n%10)

num = 909
print("Palindrome" if num == rev_num(num) else "Not Palindrome")

Python Output

Input:  
num = 909 

Output:  
Palindrome

Detailed Explanation

Problem Statement

A palindrome number is a number that reads the same whether going forward or backward. 121, 909, and 12321 are examples of palindromes, whereas 1234 is not. The problem is to determine whether a given number is a palindrome or not using recursion.

Step-by-Step Dry Run (Example: num = 121 in C)

We employ the help of a helper function revNum which constructs the reverse of the number recursively.

Call revNum(121, 0) → last digit = 1 → reverse = 0*10 + 1 = 1 → call revNum(12, 1)

Call revNum(12, 1) → last digit = 2 → reverse = 1*10 + 2 = 12 → call revNum(1, 12)

Call revNum(1, 12) → last digit = 1 → reverse = 12*10 + 1 = 121 → call revNum(0, 121)

Base case reached: return 121.

Finally, compare 121 == 121 → true → "Palindrome".

Real-Life Analogy

Think of reading a word in a mirror. If the reflected word looks exactly the same, it’s a palindrome. With numbers, reversing them is like looking at their “mirror image” and checking if it matches the original.

Why Recursion Fits This Problem

Reversing a number is a naturally repetitive process: take the bottom digit, add it to a fresh number, drop the bottom digit from the original, and do it again until there is nothing left. Recursion captures this "do the same thing with a smaller number" structure elegantly.

Complexity

Time Complexity: O(d) where d is the number of digits.

Space Complexity: O(d) because of recursion stack.

Common Mistakes

Omitting to deal with negative numbers (e.g., -121 is not a palindrome).

Not passing the rev value using a helper function.

Comparing integers while strings are needed.

Practical Uses

Palindrome checks occur in data validation algorithms (e.g., numeric IDs), in cryptography (where symmetry can be an issue), and in certain interview puzzles to verify logical thinking. 

Learning Insights

This is a wonderful problem to learn recursive thinking since the step of reversing is the same every time but on a smaller segment of the number. It also demonstrates how you can employ additional parameters in recursion to build up results without resorting to global variables.

SEO-Optimized Closing Paragraph

Verification if a number is a palindrome via recursion is a lovely programming exercise that hones your skill in function calls, base case, and problem decomposition. Through the implementation in C, C++, Java, and Python, you master language-agnostic method of reversing numbers and comparing outcomes, which is a skill essential for coding interviews as well as real-world software work that involves data verification or numeric symmetry checking.