Visual Basic

My.Resources.[Image Name here]

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Private Function ConvertDecimalToHexadecimal(ByVal number As Decimal) As String<br />
	Return Double.Parse(number).ToString("X")<br />
End Function<br />
<br />
Private Function ConvertHexadecimalToDecimal(ByVal number As String) As String<br />
	If UCase(Trim(number)).StartsWith("&H") Then number = number.Substring(2)<br />
	Return Double.Parse(number, Globalization.NumberStyles.HexNumber).ToString<br />
End Function<br />

Public Class Form1
    'Test conversion of the largest allowed decimal value
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Dim msg As String = "MaxDecimal: " & Decimal.MaxValue.ToString & _
            vbCrLf & "MaxDecimal as Hex: " & DecToHex(Decimal.MaxValue).ToUpper & _
            vbCrLf & "Hex converted back: " & HexToDec(DecToHex(Decimal.MaxValue)).ToString

        MsgBox(msg)
    End Sub

    '---MAIN CONVERSION FUNCTIONS---

    'Converts a decimal type to it's Hex value
    'Does not support fractional numbers, so don't pass them :)
    'Actually they just get rounded so nothing to worry about.
    Private Function DecToHex(ByVal number As Decimal) As String
        number = Decimal.Round(number)
        Dim result As New System.Text.StringBuilder

        Do While number > 0
            Dim remainder As Integer = number Mod 16

            number = number / 16D
            number = Decimal.Truncate(number)
            result.Insert(0, DecToHexChar(remainder))
        Loop
        Return result.ToString
    End Function

    'Converts a string of Hex characters to it's decimal equivalent
    'Does not provide any validation.  String must have nothing but
    'valid Hex values.  Although no errors should occur.
    Private Function HexToDec(ByVal hex As String) As Decimal
        Dim result As Decimal

        For i As Decimal = 0 To hex.Length - 1
            Dim chr As Char = hex.Chars(i)
            result += (HexCharToDec(chr) * Pow(16, hex.Length - 1 - i))
        Next
        Return result
    End Function

    '---HELPER FUNCTIONS---

    'Converts a Decimal value 0 to 15 to it's Hex character equivalent
    'If number is anything else it returns String.Empty
    Private Function DecToHexChar(ByVal number As Integer) As String
        If number < 10 Then Return number
        Select Case number
            Case 10 : Return "A"
            Case 11 : Return "B"
            Case 12 : Return "C"
            Case 13 : Return "D"
            Case 14 : Return "E"
            Case 15 : Return "F"
        End Select
        Return String.Empty
    End Function

    'Converts a Hex character to it's decimal equivalent
    'Valid characters: 0-9, A-F
    'Returns -1 if invalid
    Private Function HexCharToDec(ByVal chr As Char) As Decimal
        If Char.IsDigit(chr) Then Return Decimal.Parse(chr)

        Select Case Char.ToUpper(chr)
            Case "A" : Return 10D
            Case "B" : Return 11D
            Case "C" : Return 12D
            Case "D" : Return 13D
            Case "E" : Return 14D
            Case "F" : Return 15D
        End Select
        Return -1D
    End Function

    'Raises a number to a given power
    'Math.Pow and ^ were not options because they don't handle up to decimal
    Private Function Pow(ByVal number As Decimal, ByVal exponent As Integer) As Decimal
        Dim result As Decimal = 1
        For i As Integer = 1 To exponent
            result *= number
        Next
        Return result
    End Function
End Class