C ++中的回文数

Question

I'm trying to write a C++ program to find if a number is a palindrome. Here's my code. The problem is that the program returns false even when the number is a palindrome.

#include <cstdlib>
#include <iostream>
#include <string>

bool is_palindrome(int n){
  std::string num = std::to_string(n);
  int len = num.length();
  bool check = false;
  for(int i=0; i < len/2; i++){
    if(num[i] == num[len-i])
    check = true;
  }
  return check;
}

int main(){
   int num = 23232;
   std::cout<< is_palindrome(num) << std::endl;
   return 0;

}

What is my logic missing.

Answer 1

The maximum index of num array is len - 1 and not len . So use:

if (num[i] == num[len - 1 - i])

to compare the first array index to the last array index, and so on.

There is also another error since is_palindrome() will return true even if there is one coincidence (ie returns true if any 2 indices match). So when checked becomes true it never becomes false again.

You can finally change to:

for (int i = 0; i < len/2; i++)
    if (num[i] != num[len - 1 - i])
        return false;

return true;