What is wrong with my sentence palindrome code (C++)?

Question

The below code is of a sentence palindrome checker. I'm a newbie programmer so I'm having a hard time debugging this code. It's showing incorrect output. For example, if the sentence is "A man, a plan, a canal: Panama" It's giving false as a result instead of true. (Blank spaces and punctuations are to be neglected.)

---

#include <iostream>

class Solution
{
public:
    bool isPalindrome(std::string s)
    {
        int l, i;
        i = 0;
        l = s.length();

        while (i <= (l - 1))
        {

            if (s[i] == ' ' || ispunct(s[i]) == true)
                i++;

            else if (s[l - 1] == ' ' || ispunct(s[l - 1]) == true)
                l--;

            else if (tolower(s[i]) == tolower(s[l - 1]))
            {
                l--;
                i++;
            }

            else
                return false;
        }
        return true;
    }
};

int main(void)
{
    Solution s;
    const std::string text = "Panama";

    std::cout << s.isPalindrome(text);

    return 0;
}

Answer 1

The problem is very likely that the character classification functions (like e.g. ispunct) does not return a bool result.

They return an int whose value can be any non-zero value for "true".

That means the condition like ispunct(s[i]) == true might actually be false for punctuation characters.

You need to use e.g. ispunct(s[i]) != 0 (or just plain ispunct(s[i])) instead.