How do I write a proper C++ Palindrome code?

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Hello guys, I just wanted to know if the current logic palindrome is valid or not since I have seen so many other ways to solve such kind of problem. All I am asking if it is valid for me to stick with this method or not (maybe has some problems trying other examples...).

As for the runtime, it worked fine for me so far.

Code:

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

int main()
{
    int length = 0;
    char input[80]; string res;
    cout<<"Please enter a string: ";
    cin.getline(input, 80);
    
    for (length = 0; input[length] != '\0'; length++);
    
    for (int i = length - 1; i >= 0 ; i--)
    {
        res += input[i];
    }
    
    if (input == res)
    {
        cout<<input<<" is a palindrome!"<<endl;
    }
    else
    {
        cout<<input<<" is NOT a paindrome!"<<endl;
    }
    return 0;
}

Posted 14-Oct-14 12:31pm

User 8481904

Updated 14-Oct-14 12:36pm

v2

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Sergey Alexandrovich Kryukov 14-Oct-14 18:53pm

Yes, there are problems... please see Solution 1.
—SA

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Sergey Alexandrovich Kryukov · Accepted Answer · 2014-10-14T12:53:00

This at this: what happens if a user enters more than 80 characters? This is a serious problem, you have to fix it. With the type std::string, you don't have to use the char[] type at all and care about it. If you choose to use std::string, input it, not null-terminated string. Also, for std::string, you don't need to check up null character: use string::length() instead. Please review this class thoroughly: http://www.cplusplus.com/reference/string/string[^].

Also, you repeat "80" twice. This is not supportable. Define it as a constant explicitly.

You can use and compare string values, but this is not efficient. (Yes, I understand that performance is not critical at all, but aren't you do it for learning programming? This is a good reason to try to do the very best.) Here is what you can do: using a constant string, just compare two characters in a loop, starting from leftmost and rightmost character, until you reach the middle. It should work for both odd and even lengths, as well as empty string (and empty string is a palindrome). This way, you can break from the loop at first discrepancy you account, without checking up all the characters.

—SA