Roman and Arabic Numbers Conversions

[anhn]

There were many people (including in these forums) provided many different ways to convert back and fort between Roman and Arabic numbers.

Here is my version if you want it short: (Don't complain, I am lazy to write full comments)

Function RomanToArabic(ByVal Roman As String) As Integer
    '-- Convert Roman number to Arabic number
    '-- Return -32768 as an error flag if Roman string is invalid
    Dim i       As Integer
    Dim Unit    As Integer
    Dim OldUnit As Integer

    OldUnit = 1000
    For i = 1 To Len(Roman)
        Select Case UCase(Mid$(Roman, i, 1))
            Case "I":  Unit = 1
            Case "V":  Unit = 5
            Case "X":  Unit = 10
            Case "L":  Unit = 50
            Case "C":  Unit = 100
            Case "D":  Unit = 500
            Case "M":  Unit = 1000
            Case Else: '-- unaccepted Roman digit
                RomanToArabic = -32768
                Exit Function
        End Select
        If Unit > OldUnit Then RomanToArabic = RomanToArabic - 2 * OldUnit
        RomanToArabic = RomanToArabic + Unit
        OldUnit = Unit
    Next i
End Function

Function ArabicToRoman(ByVal Arabic As Integer) As String
    '-- Convert Arabic number to Roman nunber
    Const R100 = ",C,CC,CCC,CD,D,DC,DCC,DCCC,CM"
    Const R10 = ",X,XX,XXX,XL,L,LX,LXX,LXXX,XC"
    Const R1 = ",I,II,III,IV,V,VI,VII,VIII,IX"
    
    If Arabic < 0 Then      '-- this is not a proper way but
        ArabicToRoman = "-" '   provides a way to deal with
        Arabic = -Arabic    '   negative numbers instead of
    End If                  '   raising an error
    ArabicToRoman = ArabicToRoman & String$(Arabic \ 1000, "M")
    Arabic = Arabic Mod 1000
    ArabicToRoman = ArabicToRoman & Split(R100, ",")(Arabic \ 100)
    Arabic = Arabic Mod 100
    ArabicToRoman = ArabicToRoman & Split(R10, ",")(Arabic \ 10)
    Arabic = Arabic Mod 10
    ArabicToRoman = ArabicToRoman & Split(R1, ",")(Arabic)
End Function