C++ Palindrome Number Program

What Is a Palindrome Number?

A palindrome number reads the same forwards and backwards. Classic examples: 121, 3443, and every one-digit value.

n is palindrome  ⇔  reverse(digits of n) == n

Examples:
  121  → reverse 121  → yes
  123  → reverse 321  → no
    7  → reverse 7    → yes
   10  → reverse 01=1 → no

How to Check a Palindrome Number in C++

Four clear steps — then pick a math reverse or a string compare.

1. Reject negatives for this beginner rule (optional: work with abs if your problem allows it).
2. Copy n into a temporary variable.
3. Build the reverse: repeatedly take digit = temp % 10, then rev = rev * 10 + digit, then temp /= 10.
4. Compare rev with the original n.

Pseudocode

function IsPalindrome(n):
    if n < 0:
        return false

    original = n
    rev = 0

    while n > 0:
        digit = n mod 10
        rev = rev * 10 + digit
        n = n / 10

    return rev == original

Cheat Sheet

Keep these facts handy while writing the program.

Live Preview

Enter an integer to see the reversed digits and the palindrome check.

n = 121
Reverse = 121
121 is a palindrome

Worked Walkthrough — n = 121

Peel digits from the right and push them onto the reverse value.

original = 121
rev = 0

Step 1: digit = 1, rev = 0*10 + 1 = 1,   n = 12
Step 2: digit = 2, rev = 1*10 + 2 = 12,  n = 1
Step 3: digit = 1, rev = 12*10 + 1 = 121, n = 0

rev == original → 121 is a palindrome

C++ Programs

Start with the math reverse — interviewers usually want that. Use the string version when readability matters more than avoiding text helpers.

#include <iostream>
using namespace std;

bool isPalindrome(int n)
{
    if (n < 0)
    {
        return false;
    }

    int original = n;
    int rev = 0;

    while (n > 0)
    {
        int digit = n % 10;
        rev = rev * 10 + digit;
        n /= 10;
    }

    return rev == original;
}

int main()
{
    int number = 121;
    cout << number
         << (isPalindrome(number) ? " is a palindrome" : " is not a palindrome")
         << endl;
    return 0;
}

121 is a palindrome

#include <iostream>
#include <string>
#include <algorithm>
using namespace std;

bool isPalindrome(int n)
{
    if (n < 0)
    {
        return false;
    }

    string s = to_string(n);
    string rev = s;
    reverse(rev.begin(), rev.end());

    return s == rev;
}

int main()
{
    cout << (isPalindrome(121) ? "true" : "false") << endl;
    cout << (isPalindrome(123) ? "true" : "false") << endl;
    cout << (isPalindrome(7) ? "true" : "false") << endl;
    cout << (isPalindrome(-121) ? "true" : "false") << endl;
    return 0;
}

true
false
true
false

Time and Space Complexity

Here d is the digit count. Both scan the digits once; the string method allocates character storage.

Key Takeaways