/**
 * encode codeword - Encode standard input using the given codeword.
 */

// +---------+--------------------------------------------------------
// | Headers |
// +---------+

#include <stdio.h>	// For getchar and printf
#include <string.h>	// For strlen


// +-----------+------------------------------------------------------
// | Constants |
// +-----------+

/**
 * The minimum and maximum printable characters.
 */
#define MIN_CHAR 32
#define MAX_CHAR 127


/**
 * The default codeword (in case one does not get specified on the
 * command line.
 */
#define DEFAULT_CODEWORD "CSC161-01"


// +------+-----------------------------------------------------------
// | Main |
// +------+

int
main (int argc, char *argv[])
{
  char *codeword;	// The codeword we're using
  int ch;		// The input character
  int k;		// The character in the codeword
  int e;                // The encoded character
  int i=0;		// The index in the codeword
  int len;		// The length of the codeword
  int printable;	// The number of printable characters

  // Set up information on the codeword
  if (argc < 2)
    codeword = DEFAULT_CODEWORD;
  else
    codeword = argv[1];
  len = strlen (codeword);

  // Determine the number of printable characters
  printable = 1 + MAX_CHAR - MIN_CHAR;

  // Process the input
  while ((ch = getchar ()) != EOF)
    {
      // Echo non-printable characters verbatim
      if ((ch < MIN_CHAR) || (ch > MAX_CHAR))
        printf ("%c", ch);
      else
        {
          // Get the next character in the code word.
          k = codeword[i];
          i = (i + 1) % len;
	  // printf ("ch=%d(%c), k=%d(%c), ", ch, ch, k, k);	// TESTING
          // Convert each to a reasonable range
          ch -= MIN_CHAR;
          k -= MIN_CHAR;
          // Add them together
          e = (ch + k) % printable;
          //  Return to a reasonable range
          e += MIN_CHAR;
          // And print it out
          // printf ("e=%d(%c)\n", e, e);				// TESTING
          printf ("%c", e);
        }
    } // while

  // And we're done
  return 0;
} // main