Palindrome tester has logic flaws

Question

This is just a basic palindrome tester for my C++ class, and there appears to be issues.

I already know that I have two separate flaws in here somewhere. At least one, I strongly suspect, is a logic issue. The first problem is that it runs fine the first time through, but when the loop initiates, it doesn't ask for user input to put in a new line to test as a palindrome, it simply retests the old one. The second issue is, I assume, that it is testing spaces, which I base off the fact that it's giving 'hannah' back as good, but 'never even or odd' comes back bad. This one I just don't know how to fix.

#include <iostream>
#include <string>

using namespace std;

int main()
{
  bool repeater = true;
  do
    {
      string palindroneCheck;
      bool palindronity = true;

      cout << "Please enter a line to test for palindromity.\n";
      getline(cin, palindroneCheck);

      int stringSize = palindroneCheck.size();
      int cutOff = stringSize/2;

      for (int palindroneLength = 0; palindroneLength < cutOff; palindroneLength++)
        {
          if (palindroneCheck[palindroneLength] != palindroneCheck[stringSize - palindroneLength -1])
            {palindronity = false;
              break;}
        }

      if(palindronity == true)
        cout << "Congratulations! This line is a palindrone!\n\n";
      else
        cout << "Sorry, but this is not a palindrone.\n\n";

      palindroneCheck.clear();

      char repeat;
      cout << "Would you like to try another line? Y/N\n";
      cin >> repeat;
      if (repeat == "n" || repeat == "N")
        repeater = false;
    } while (repeater == true);

}

One's really easy to find info on: http://stackoverflow.com/search?q=%20getline%20skipping — chris, Sep 27 '13 at 01:24
Yes chris, but not all of those have good answers. Here's a good one: http://stackoverflow.com/a/9336347/103167 — Ben Voigt, Sep 27 '13 at 01:29
I assume you meant to test `never even` (without the "or odd")? — Ben Voigt, Sep 27 '13 at 01:30

score 1 · Answer 1 · answered Sep 27 '13 at 01:28

1

OK, you are right about the spaces. Your code will demand that spaces are in the same location like every other character.

The other bug seems more subtle: it's where you ask to repeat or not.

Why? Because it asks, you enter 'n' and then 'enter'

The cin >> repeat only reads the 'n', but not the 'enter'

so the next time you do `readline(cin,PalindromCheck)' it will read an empty string.

Try to write palindromCheck just after reading it. You'll see.

answered Sep 27 '13 at 01:28

rabensky

2,864
13
18

Helpful comment, but I don't see an answer in here anywhere, not even a suggestion of what approach to take to solve the problem (which is probably appropriate for a homework question) – Ben Voigt Sep 27 '13 at 01:32
@BenVoigt Actually, showing where the problem lies is quite a good start to solving the problem. – rabensky Sep 27 '13 at 01:33
To be honest, showing me where the problem is for my logic issue is GREAT, it's my preferred way of learning. You learn my screwing up and having someone say "Here's where you f-ed the poop". Figured this part out on my own. My solution was to use 'getline(cin, repeat) for the input, then use 'repeat[0] == n' for the if statement. Works great, thanks! Working on the other part, thanks for the confirmation. – Dragon Orb XIII Sep 27 '13 at 03:22

CS Pei · Answer 2 · 2013-09-27T13:02:59.290

The reading issue of getline is solved by comments. For the whitespaces, you can tackle it by removing all the spaces inside string palindroneCheck,

std::string::iterator new_end = std::remove(palindroneCheck.begin(), palindroneCheck.end(), ' ');
std::string palindroneCheckWithoutSpaces(palindroneCheck.begin(), new_end);

Then you use palindroneCheckWithoutSpaces to do the Palindrone test.

  int stringSize = palindroneCheckWithoutSpaces.size();
  int cutOff = stringSize/2;

  for (int palindroneLength = 0; palindroneLength < cutOff; palindroneLength++)
    {
      if (palindroneCheckWithoutSpaces[palindroneLength] != palindroneCheck[stringSize - palindroneLength -1])
        {palindronity = false;
          break;}
    }

  if(palindronity == true)
    cout << "Congratulations! This line is a palindrone!\n\n";
  else
    cout << "Sorry, but this is not a palindrone.\n\n";

(you need header algorithm to use remove)

Update:

std::remove remove an element from the input range (this is defined by begin and end here) based on the value you passed in , here is the whitespace ' '. Then it return the new end of the changed range (since you delete something, the range becomes smaller). The new range starts with begin and ends with the returned value.

So the second line you create a new string based on the new range.

OK, excellent! This works (I did give citation for this). Now, I have one important question: What, exactly, did those two lines do? I mean, it's great that they worked, but I have no idea what just happened, and I'd like to understand it so I can do it on my own in the future. Please take note that this is my first C++ class, and that the only other programing class I took was same level of Python. — Dragon Orb XIII, Sep 27 '13 at 04:16

Palindrome tester has logic flaws

2 Answers2