/* Written by Kevin Klenk                                                */
/* May 5th, 1998                                                         */
/* cmps012a - Spring 1998                                                */
/* Ira Pohl                                                              */
/* This program inputs characters using getchar() until EOF is           */
/*  encountered.  It encrypts each character if it is an alphabetic      */
/*  character using the following mapping:                               */
/*                      'a' - 'z' to 'a' - 'z'                           */
/*                      'A' - 'Z' to 'A' - 'Z'                           */

#include <stdlib.h>
#include <stdio.h>
#include <ctype.h>

#define SEED 5

int main(void)
{
   char c, encryptedc;   /* Character read from input, encrypted character */

   /* Initialize the random number generator with SEED.                    */
   /* This must be done so that the pseudo-random number generator has a   */
   /*  place to start.  It does not matter what value SEED is as long as   */
   /*  it is a valid integer.  Also, you should know that, if you try to   */
   /*  decrypt your encrypted string you have to know the seed.            */
   srand(SEED);

   /* Begin main loop.  Read characters and encrypt them as long as EOF is */
   /*  not reached.  Note: only alphabetic characters are encrypted.       */
   printf("Enter some characters (Ctrl-d to exit):  ");
   while ( (c = getchar()) != EOF)
   {
      if (isupper(c))
      {
         /* Character c is an uppercase letter.     */
         /* Encrypt it to another uppercase letter. */
         encryptedc = (c + rand()) % 26 + 65;
      }
      else if (islower(c))
      {
         /* Character c is a lowercase letter.      */
         /* Encrypt it to another lowercase letter. */
         encryptedc = (c + rand()) % 26 + 97;
      }
      else
      {
         /* Character c is not alphabetic (not a letter). */
         /* Do not encrypt the character.                 */
         encryptedc = c;
      }
      putchar(encryptedc);
   }

   return 0;
}