Converting integers to roman numerals

Question

I\'m trying to write a function that converts numbers to roman numerals. This is my code so far; however, it only works with numbers that are less than 400. Is there a quick

Answer 1

    # checks if given roman number is valid, empty means 0
Function IsRoman {

    [OutputType([Boolean])]
    Param([String] $roman)

    return ($roman -ne $Null) -and ($roman -match ("^M{0,3}(CM|CD|D?C{0,3})(XC|XL|L?X{0,3})(IX|IV|V?I{0,3})$"));
}

# checks if given arabic number is valid, less than 0 or floating point is not possible and means error
Function IsConvertibleToRoman {

    [OutputType([Boolean])]
    Param([String] $arabic)

    Try {
        $result = $arabic -match "^\-?(\d+\.?\d*)(e\-?\d+)?$" -and [Double]$arabic -eq [Long]$arabic -and [Long]$arabic -ge 0;
    }
    Catch {
        # this extra check is necessary because conversion to double fails with hex numbers
        return $arabic -match "^0x[0-9a-f]+$";
    }

    return $result;
}

# convert arabic numerals into roman numerals, including validity check, allow three ciphres as maximum
Function ArabicToRoman {

    [OutputType([String])]
    Param([String] $arabicNumber)

    If (-not (IsConvertibleToRoman $arabicNumber)) {
        [String]$errorMessage = "can not convert '$arabicNumber' into roman number!";

        Write-Error $errorMessage -Category InvalidArgument;

        return $Null;
    }

    [Long]$number = $arabicNumber;

    # ---------------------------------------------------------------
    [String]$romanNumber = "M"*([math]::Floor($number / 1000));
    # ---------------------------------------------------------------
    $number = $number % 1000;

    If ($number -ge 500) {
        If ($number -ge 900) {
            $romanNumber = $romanNumber + "CM";
            $number = $number - 900;
        } Else {
            $romanNumber = $romanNumber + "D";
            $number = $number - 500;
        }
    }

    If ($number -lt 400) {
        $romanNumber = $romanNumber + "C"*([math]::Floor($number / 100));
    } Else {
        $romanNumber = $romanNumber + "CD";
    }
    # ---------------------------------------------------------------
    $number = $number % 100;

    If ($number -ge 50) {
        If ($number -ge 90) {
            $romanNumber = $romanNumber + "XC";
            $number = $number - 90;
        } Else {
            $romanNumber = $romanNumber + "L";
            $number = $number - 50;
        }
    }

    If ($number -lt 40) {
        $romanNumber = $romanNumber + "X"*([math]::Floor($number / 10));
    } Else {
        $romanNumber = $romanNumber + "XL";
    }
    # ---------------------------------------------------------------
    $number = $number % 10;

    If ($number -ge 5) {
        If ($number -eq 9) {
            $romanNumber = $romanNumber + "IX";
            return $romanNumber;
        } Else {
            $romanNumber = $romanNumber + "V";
            $number = $number - 5;
        }
    }

    If ($number -lt 4) {
        $romanNumber = $romanNumber + "I"*$number;
    } Else {
        $romanNumber = $romanNumber + "IV";
    }
    # ---------------------------------------------------------------

    return $romanNumber;
}

# convert roman numerals into arabic numerals, including validity check, evaluation from left to right
Function RomanToArabic {

    [OutputType([Int])]
    Param([String] $romanNumber)

    [long]$arab = 0;
    [char]$lastCipher = $Null;

    If (-not (isRoman $romanNumber)) {
        [String]$errorMessage = "'$romanNumber' is not a roman numeral!";

        Write-Error $errorMessage -Category InvalidArgument

        return -1;
    }

    Foreach($aCipher In $romanNumber.ToUpper().ToCharArray()) {
        Switch ($aCipher) {
            'I' {
                $arab += 1;
                Break;
            }
            'V' {
                If ($lastCipher -eq 'I') {
                    $arab += 4 - 1;
                } Else {
                    $arab += 5;
                }
                Break;
            }
            'X' {
                If ($lastCipher -eq 'I') {
                    $arab += 9 - 1;
                } Else {
                    $arab += 10;
                }
                Break;
            }
            'L' {
                If ($lastCipher -eq 'X') {
                    $arab += 40 - 10;
                } Else {
                    $arab += 50;
                }
                Break;
            }
            'C' {
                If ($lastCipher -eq 'X') {
                    $arab += 90 - 10;
                } Else {
                    $arab += 100;
                }
                Break;
            }
            'D' {
                If ($lastCipher -eq 'C') {
                    $arab += 400 - 100;
                } Else {
                    $arab += 500;
                }
                Break;
            }
            'M' {
                If ($lastCipher -eq 'C') {
                    $arab += 900 - 100;
                } Else {
                    $arab += 1000;
                }
                Break;
            }
        }

        $lastCipher = $aCipher;
    }

    return $arab;
}

Please have a look here for further information:

https://github.com/CBM6502/Conversion-Test