Number Systems

    And finally, we come to Roman Numerals.  They are roughly equivelent to something that we would write as "100 + 50 + 10 + 1".  In other words, they are baseless.

'The following are  the 14 different valid letter combinations_
'for Roman Numerals
'and what they equal.  It is improper (for whatever reason) to_
'say "IM = 999",
'you must say "CMXCIX".

Public Enum RomanNumerals As Integer
   N = 0
   I = 1
   IV = 4
   V = 5
   IX = 9
   X = 10
   XL = 40
   L = 50
   XC = 90
   C = 100
   CD = 400
   D = 500
   CM = 900
   M = 1000
End Enum

Public Function FromRomanNumeral(ByVal Number As String) As Long
   Number = Number.ToUpper

   Dim chrRomans() As Char = Number.ToCharArray
   Dim intRomanParse(Number.Length) As Integer
   Dim lRoman As Long
   Dim i As Integer
   Dim iCounter As Int16
          
   'Basically, steps through the Roman Numeral string looking for
   'valuesin the RomanNumerals Enum
   For i = Number.Length - 1 To 0 Step -1
      Select Case chrRomans(i).ToString
         Case "N" '0      
            intRomanParse(i) = RomanNumerals.N

         Case "I" '1
            intRomanParse(i) = RomanNumerals.I

         Case "V" '5
            If i > 0 AndAlso chrRomans(i - 1).ToString = "I" Then
               intRomanParse(i) = RomanNumerals.IV    
               'Used if an extended digit is present since they use_
	       '2 letters     
               i -= 1
            Else  
               intRomanParse(i) = RomanNumerals.V
            End If

         Case "X" '10
            If i > 0 AndAlso chrRomans(i - 1).ToString = "I" Then
               intRomanParse(i) = RomanNumerals.IX    
               'Used if an extended digit is present since they use_
	       '2 letters        
               i -= 1
            Else
               intRomanParse(i) = RomanNumerals.X  
            End If

         Case "L" '50
            If i > 0 AndAlso chrRomans(i - 1).ToString = "X" Then
               intRomanParse(i) = RomanNumerals.XL   
               'Used if an extended digit is present since they use_
	       '2 letters
               i -= 1
            Else
               intRomanParse(i) = RomanNumerals.L
            End If

         Case "C" '100      
            If i > 0 AndAlso chrRomans(i - 1).ToString = "X" Then
               intRomanParse(i) = RomanNumerals.XC     
               'Used if an extended digit is present since they use_
	       '2 letters 
               i -= 1    
            Else   
               intRomanParse(i) = RomanNumerals.C
            End If

         Case "D" '500                     
            If i > 0 AndAlso chrRomans(i - 1).ToString = "C" Then
               intRomanParse(i) = RomanNumerals.CD         
               'Used if an extended digit is present since they use_
	       '2 letters           
               i -= 1      
            Else
               intRomanParse(i) = RomanNumerals.D
            End If

         Case "M" '1000     
            If i > 0 AndAlso chrRomans(i - 1).ToString = "C" Then
               intRomanParse(i) = RomanNumerals.CM
               'Used if an extended digit is present since they use_
	       '2 letters 
               i -= 1 
            Else
               intRomanParse(i) = RomanNumerals.M
            End If

         Case Else 'Not a digit    
            Throw New Exception(Number & " is not a valid Roman_
		Numeral because it contains the symbol:_
		" & chrRomans(i).ToString & ".")
      End Select

   Next

   For i = 0 To Number.Length
      lRoman += intRomanParse(i)
   Next

   Return lRoman
End Function

Public Function ToRomanNumeral(ByVal Number As Long) As String
   Dim strRoman As String
   Dim intM, intCM, intD, intCD, intC, intXC, intL, intXL, intX,_
	intIX, intV, intIV, intI As Short
   Dim i As Short

   If Number = 0 Then Return "N"

   'How many integral times does "M" go into the number?
   intM = Number \ RomanNumerals.M
   Number -= intM * RomanNumerals.M

   'How many integral times does "CM" go into the number?
   intCM = Number \ RomanNumerals.CM
   Number -= intCM * RomanNumerals.CM

   'How many integral times does "D" go into the number?
   intD = Number \ RomanNumerals.D
   Number -= intD * RomanNumerals.D

   'How many integral times does "CD" go into the number?
   intCD = Number \ RomanNumerals.CD
   Number -= intCD * RomanNumerals.CD

   'How many integral times does "C" go into the number?
   intC = Number \ RomanNumerals.C
   Number -= intC * RomanNumerals.C

   'How many integral times does "XC" go into the number?
   intXC = Number \ RomanNumerals.XC
   Number -= intXC * RomanNumerals.XC

   'How many integral times does "L" go into the number?
   intL = Number \ RomanNumerals.L
   Number -= intL * RomanNumerals.L

   'How many integral times does "XL" go into the number?
   intXL = Number \ RomanNumerals.XL
   Number -= intXL * RomanNumerals.XL

   'How many integral times does "X" go into the number?
   intX = Number \ RomanNumerals.X
   Number -= intX * RomanNumerals.X

   'How many integral times does "IX" go into the number?
   intIX = Number \ RomanNumerals.IX
   Number -= intIX * RomanNumerals.IX

   'How many integral times does "V" go into the number?
   intV = Number \ RomanNumerals.V
   Number -= intV * RomanNumerals.V

   'How many integral times does "IV" go into the number?
   intIV = Number \ RomanNumerals.IV
   Number -= intIV * RomanNumerals.IV

   'How many integral times does "I" go into the number?
   intI = Number \ RomanNumerals.I
   Number -= intI * RomanNumerals.I


   'Puts together all the pieces
   For i = 1 To intM
      strRoman &= "M"
   Next

   For i = 1 To intCM
      strRoman &= "CM"
   Next

   For i = 1 To intD
      strRoman &= "D"
   Next

   For i = 1 To intCD
      strRoman &= "CD"
   Next

   For i = 1 To intC
      strRoman &= "C"
   Next

   For i = 1 To intXC
      strRoman &= "XC"
   Next

   For i = 1 To intL
      strRoman &= "L"
   Next

   For i = 1 To intXL
      strRoman &= "XL"
   Next

   For i = 1 To intX
      strRoman &= "X"
   Next

   For i = 1 To intIX
      strRoman &= "IX"
   Next

   For i = 1 To intV
      strRoman &= "V"
   Next

   For i = 1 To intIV
      strRoman &= "IV"
   Next

   For i = 1 To intI
      strRoman &= "I"
   Next

   Return strRoman
End Function

'This function will take an incorrectly formated Roman Numeral and_
'return it in it's corrected form ("CMXCIXVIII" becomes "MVII")
Public Function CorrectRomanNumeral(ByVal Number As String) As String
   Dim lRoman As Long = FromRomanNumeral(Number)
   Return ToRomanNumeral(lRoman)
End Function