How to solve the Palindrome Problem in C++

[Coreycoder]

I'm having trouble writing a C++ program to determine whether a number is a palindrome. My code is returning false even when the number is a palindrome. For instance, 12321 is a palindrome number, but 1451 is not.

bool checkPalindrome(int original) {

  int reverseNum = 0;
  int tempOriginal = original;

  while (tempOriginal > 0) {

    int lastDigit = tempOriginal % 10;
    reverseNum = reverseNum * 10 + lastDigit;
    tempOriginal = tempOriginal / 10;
  }

  if (original == reverseNum) {
    return true;
  } else {
    return false;
  }
}

Can anyone confirm if the code referenced from this is correct?

[2kaud]

Consider as C++20:

#include <iostream>
#include <iterator>
#include <format>
#include <concepts>

using fmt_to = std::ostream_iterator<char>;
const auto fmt_cout { fmt_to(std::cout) };

bool checkPalindrome(std::unsigned_integral auto original) {
	unsigned reverseNum {};

	for (auto tempOriginal { original }; tempOriginal > 0; tempOriginal /= 10)
		reverseNum = reverseNum * 10 + tempOriginal % 10;

	return original == reverseNum;
}

int main() {
	constexpr const auto fmt { "{:>5}  {}\n" };

	for (const unsigned i : {12321, 1451, 1, 23, 22})
		std::format_to(fmt_cout, fmt, i, checkPalindrome(i));
}

which displays:

12321  true
 1451  false
    1  true
   23  false
   22  true

[2kaud]

Another approach is to convert the number to a std::string and then check that this is a palindrome. Consider:

bool checkPalindrome(std::unsigned_integral auto original) {
	const auto str { std::to_string(original) };

	return str == std::string { str.rbegin(), str.rend() };
}

or using std::ranges:

bool checkPalindrome(std::unsigned_integral auto original) {
	const auto str { std::to_string(original) };

	return str == std::ranges::to<std::string>(str | std::views::reverse);
}