MODULE RomanNumerals;
FROM InOut IMPORT WriteString, WriteCard, WriteLn;
FROM Strings IMPORT Length;

(* Convert given Roman numeral to binary *)
PROCEDURE DecodeRoman(s: ARRAY OF CHAR): CARDINAL;
    VAR i, d, len, acc: CARDINAL;

    PROCEDURE Digit(d: CHAR): CARDINAL;
    BEGIN
        CASE CHR( BITSET(ORD(d)) + BITSET{5} ) OF (* lowercase *)
            'm': RETURN 1000;
        |   'd': RETURN 500;
        |   'c': RETURN 100;
        |   'l': RETURN 50;
        |   'x': RETURN 10;
        |   'v': RETURN 5;
        |   'i': RETURN 1;
        ELSE
            RETURN 0;
        END;
    END Digit;
BEGIN
    len := Length(s);
    acc := 0;
    FOR i := 0 TO len-1 DO
        d := Digit(s[i]);
        IF d=0 THEN RETURN 0; END;

        IF (i # len-1) AND (d < Digit(s[i+1])) THEN
            acc := acc - d;
        ELSE
            acc := acc + d;
        END;
    END;
    RETURN acc;
END DecodeRoman;

PROCEDURE Show(s: ARRAY OF CHAR);
BEGIN
    WriteString(s);
    WriteString(": ");
    WriteCard(DecodeRoman(s), 0);
    WriteLn();
END Show;

BEGIN
    Show("MCMXC");
    Show("MDCLXVI");
    Show("mmvii");
    Show("mmxxi");
END RomanNumerals.