/* Filename:  PalindromeCString.cpp

   Author:  Br. David Carlson

   Date:  December 4, 2006

   This program repeatedly has the user input a string and for each checks to see if it
   is or is not a palindrome.  It then prints the result of this test before asking the
   user whether to do another string.

   Tested with:
      Microsoft Visual C++ .NET 2003
      g++ under Linux
*/

#include <iostream>
using namespace std;

const int StringMax = 82;
typedef char StringType[StringMax];

// Function prototype:
bool IsPalindrome(StringType Sample);


int main(void)
   {
   StringType Sample, Response;
   char ResponseLetter;
   
   do
      {
      cout << "Enter the string to be checked to see if it is a palindrome:" << endl;
      cin.getline(Sample, StringMax);

      if (IsPalindrome(Sample))
         cout << Sample << " is a palindrome." << endl;
      else
         cout << Sample << " is NOT a palindrome." << endl;
         
      cout << "Check another string (y/n)? ";
      cin.getline(Response, StringMax);
      
      if (strlen(Response) > 0)  // get the first letter
         ResponseLetter = Response[0];
      else  // assume that the answer is no
         ResponseLetter = 'n';
      }
   while ((ResponseLetter == 'y') || (ResponseLetter == 'Y'));
   
   return 0;
   }

/*  Given:  Sample    A C-string of type StringType.
    Task:   To decide if Sample holds a palindrome, a string that reads the same 
            forwards as backwards.
    Return: In the function name, it returns true if Sample is a palindrome;
            false otherwise.
 */
bool IsPalindrome(StringType Sample)
   {
   int Length, MidPoint, ForwardStop, ForwardIndex, BackwardIndex;
   
   Length = strlen(Sample);
   if (Length < 2)  // then Sample is trivially a palindrome
      return true;
      
   MidPoint = (Length - 1) / 2;
   
   if (2 * MidPoint + 1 == Length)  // then Length is odd
      ForwardStop = MidPoint - 1;   // Ignore the middle character.
   else   // Length is even
      ForwardStop = MidPoint;
   
   BackwardIndex = Length - 1;
   for (ForwardIndex = 0; ForwardIndex <= ForwardStop; ForwardIndex++)
      {
      if (Sample[ForwardIndex] != Sample[BackwardIndex])
         return false;
         
      BackwardIndex--;
      }
   
   return true;
   }