void convert_string(char *expr , char cleaned[MAX_STRING_SIZE])
{/* change to all lower case
     remove spaces and punctuation */
     int i=0, count=0;
     char ch;
     while (i < strlen(expr)) {
        if (isspace(expr[i])) i++;
         else if (ispunct(expr[i])) i++;
         else {
          ch = expr[i++];
          cleaned[count++] = tolower(ch);
        }
    }
    cleaned[count] = '\0';
}

int parser(char expr [])
{
   int i=0, half, odd;
   char ch;
   stack_ptr top = NULL;
   half = (int)strlen(expr)/2;
   odd = strlen(expr)%2;
   while (i < half) /* push half the letters onto the stack */
       push(&top, expr[i++]);
  if (odd) i++; 
   while (i < strlen(expr))
   {/* pop character from stack and compare with next character in the string */
      ch = pop(&top);
      if (expr[i] != ch)
      {/* not a palindrome, empty out stack and return false */
          while (!IS_EMPTY(top)) {
             ch = pop(&top);
          }
          return FALSE;
      }
      i++;
      return TRUE;
    }
}
    

int main()
{
   char expr [MAX_STRING_SIZE];
   char parse_string [MAX_STRING_SIZE];
   int i, half, odd, ok_pal;
   stack_ptr top = NULL;
   do {
      printf("Expression: ");
      /* use fgets to read in strings with spaces,
         strip off the new line character to get the correct count */
      fgets(expr, MAX_STRING_SIZE,stdin);
      if (expr[strlen(expr)-1] == '\n')
          expr[strlen(expr)-1] = '\0';
      if(strlen(expr)) {
        convert_string(expr, parse_string);
        printf("cleaned %s\n", parse_string);
        if(ok_pal = parser(parse_string))
          printf("%s IS a palindrome.\n\n", expr);
       else
          printf("%s IS NOT a palindrome.\n\n", expr);
       }
   }while (strlen(expr));
}