#include <stdio.h>
#include <ctype.h>
#include <string.h>
#include "checkit.h"

int rot_13(unsigned char i)
{
   if ((i >= 'A' && i <= 'M') || (i >= 'a' && i <= 'm'))
   {
      i = i + 13;
   }
   else if ((i >= 'N' && i <= 'Z') || (i >= 'n' && i <= 'z'))
   {
      i = i - 13;
   }
   else if (i == '\n')
   {
      printf("Invalid input.\n");
   }

   return i;
}

void test_cases(void)
{

 /*  checkit_string(rot_13("abcd"), "nopq");
   checkit_string(rot_13("hello", uryyb);
   checkit_string(rot_13("Clarence", Pynerapr);*/
}

int user_interaction()
{
   unsigned char i;

   printf("Please enter a character string.\n");
   i = 50;

   i = getchar();
   while (i != EOF)
   {
      printf("%c", rot_13(i));
      i = getchar();
   }

   return 0;
}

int main(void)
{
   test_cases();
   user_interaction();

   return 0;
}