{
  Author:  Douglas Jones
  Purpose: Convert between normal text and rotate-13 Caesar cypher text
}
PROGRAM mp2(input,output);
  VAR
    ch: char;

  PROCEDURE rot13(VAR c: char);

    FUNCTION isupper(ch: char): boolean;
      BEGIN
        isupper := (ch >= 'A') and (ch <= 'Z');
      END; { isupper }

    FUNCTION islower(ch: char): boolean;
      BEGIN
        islower := (ch >= 'a') and (ch <= 'z');
      END; { isupper }

    BEGIN { rot13 }
      IF isupper(c)
        THEN
          c := chr( (ord(c) - ord('A') + 13) mod 26 + ord('A') )
        ELSE
          IF islower(c)
            THEN
              c := chr( (ord(c) - ord('a') + 13) mod 26 + ord('a') )
            ELSE
              c := c;
    END; { rot13 }

  BEGIN { mp2 }
    WHILE not(eof) DO
      BEGIN
        WHILE not(eoln) DO
          BEGIN
            read(ch);
            rot13(ch);
            write(ch);
          END;
        readln;
        writeln;
      END;
  END. { mp2 }