Roman Numerals - Conversion to/from

[dbasnett]

Code to aid in the conversion of standard Roman Numerals (1 - 3,999).

Public Class RomanNumeral
    Enum Roman
        M = 1000
        CM = 900
        D = 500
        CD = 400
        C = 100
        XC = 90
        L = 50
        XL = 40
        X = 10
        IX = 9
        V = 5
        IV = 4
        I = 1
    End Enum

    Private Shared Translation As List(Of Roman) = [Enum].GetValues(GetType(Roman)).OfType(Of Roman).OrderByDescending(Function(t) t).ToList

    Public Shared Function ToRoman(num As Integer) As String
        Dim rv As New System.Text.StringBuilder
        For Each t As Roman In Translation
            If num <= 0 Then Exit For
            While num >= t
                num -= t
                rv.Append(t.ToString)
            End While
        Next
        Return rv.ToString
    End Function

    Public Shared Function FromRoman(num As String) As Integer
        Dim rv As Integer
        For Each t As Roman In Translation
            If num = "" Then Exit For
            While num.StartsWith(t.ToString)
                rv += t
                num = num.Remove(0, t.ToString.Length)
            End While
        Next
        Return rv
    End Function

    Public Shared Function ToXMLTable() As XElement
        Dim root As XElement = <RomanNumerals></RomanNumerals>
        Dim entry As XElement = <number>
                                    <value></value>
                                    <roman></roman>
                                </number>
        Dim rv As New XElement(root)
        For x As Integer = 1 To 3999
            Dim ent As New XElement(entry)
            ent.<value>.Value = x.ToString
            ent.<roman>.Value = ToRoman(x)
            rv.Add(ent)
        Next
        Return rv
    End Function
End Class

To test:

    Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
        Dim foo As XElement = RomanNumeral.ToXMLTable
        For Each xe As XElement In foo.Elements
            Dim r As String = xe.<roman>.Value
            Dim rc As Integer = RomanNumeral.FromRoman(r)
            Debug.WriteLine("{0,4} {1,-16} {2,4}  {3}", xe.<value>.Value, r, rc.ToString, rc.ToString = xe.<value>.Value)
        Next
    End Sub