Roman Numeral in Algol68

Welcome to the Roman Numeral in Algol68 page! Here, you'll find the source code for this program as well as a description of how the program works.

Current Solution

PROC usage = VOID: printf(($gl$, "Usage: please provide a string of roman numerals"));
PROC error = VOID: printf(($gl$, "Error: invalid string of roman numerals"));

# Roman numeral table #
MODE ROMAN = STRUCT(CHAR letter, INT value);
[]ROMAN romans = (
    ("M", 1000),
    ("D", 500),
    ("C", 100),
    ("L", 50),
    ("X", 10),
    ("V", 5),
    ("I", 1)
);

# Get value of Roman letter #
PROC get roman = (CHAR letter) INT:
(
    INT value := 0;
    FOR k TO UPB romans
    WHILE value < 1
    DO
        IF (letter OF romans[k]) = letter
        THEN
            value := value OF romans[k]
        FI
    OD;

    value
);

# Convert Roman numeral to a value #
PROC roman number = (STRING s) INT:
(
    INT total := 0;
    INT prev value := -1; # No previous value #
    FOR k TO UPB s
    WHILE total >= 0
    DO
        # Get value of current letter. If not found, indicate invalid and exit #
        INT value := get roman(s[k]);
        IF value < 1
        THEN
            total := -1
        ELSE
            # Add value to total #
            total +:= value;

            # If there is a previous value and value is greater than previous value, #
            # subtract two times previous value from total to compensate for addition of #
            # previous value -- e.g., if previous value was 100 (C) and current value is #
            # 1000 (M), the total currently equals 1100, but we want it to be 900 (1100 - 2*100). #
            # Also, reset the current value so that there is no previous value #
            IF prev value > 0 AND value > prev value
            THEN
                total -:= 2 * prev value;
                value := -1
            FI;

            # Store current value to previous value #
            prev value := value
        FI
    OD;

    total
);
    
# If too few arguments, exit #
IF argc < 4
THEN
    usage;
    stop
FI;

# Convert Roman numeral to value #
STRING s := argv(4);
INT value := roman number(s);

# Display if valid, else show error message #
IF value >= 0
THEN
    printf(($gl$, whole(value, 0)))
ELSE
    error
FI

Roman Numeral in Algol68 was written by:

• rzuckerm

If you see anything you'd like to change or update, please consider contributing.

How to Implement the Solution

No 'How to Implement the Solution' section available. Please consider contributing.

How to Run the Solution

No 'How to Run the Solution' section available. Please consider contributing.