MODULE Caesar;
IMPORT
  Out;
CONST
  encode* = 1;
  decode* = -1;

VAR
  text,cipher: POINTER TO ARRAY OF CHAR;

  PROCEDURE Cipher*(txt: ARRAY OF CHAR; key: INTEGER; op: INTEGER; VAR cipher: ARRAY OF CHAR);
  VAR
    i: LONGINT;
  BEGIN
    i := 0;
    WHILE i < LEN(txt) - 1 DO
      IF (txt[i] >= 'A') & (txt[i] <= 'Z') THEN
        cipher[i] := CHR(ORD('A') + ((ORD(txt[i]) - ORD('A') + (key * op))) MOD 26)
      ELSIF (txt[i] >= 'a') & (txt[i] <= 'z') THEN
        cipher[i] := CHR(ORD('a') + ((ORD(txt[i]) - ORD('a') + (key * op))) MOD 26)
      ELSE
        cipher[i] := txt[i]
      END;
      INC(i)
    END;
    cipher[i] := 0X
  END Cipher;

BEGIN
  NEW(text,3);NEW(cipher,3);
  COPY("HI",text^);
  Out.String(text^);Out.String(" =e=> ");
  Cipher(text^,2,encode,cipher^);
  Out.String(cipher^);

  COPY(cipher^,text^);
  Cipher(text^,2,decode,cipher^);
  Out.String(" =d=> ");Out.String(cipher^);Out.Ln;

  COPY("ZA",text^);
  Out.String(text^);Out.String(" =e=> ");
  Cipher(text^,2,encode,cipher^);
  Out.String(cipher^);

  COPY(cipher^,text^);
  Cipher(text^,2,decode,cipher^);
  Out.String(" =d=> ");Out.String(cipher^);Out.Ln;

  NEW(text,37);NEW(cipher,37);
  COPY("The five boxing wizards jump quickly",text^);
  Out.String(text^);Out.String(" =e=> ");
  Cipher(text^,3,encode,cipher^);
  Out.String(cipher^);

  COPY(cipher^,text^);
  Cipher(text^,3,decode,cipher^);
  Out.String(" =d=> ");Out.String(cipher^);Out.Ln;

END Caesar.