Hi I am trying to make some code to collect tokens of a string. but I keep getting an out of range error, tho it works with some expressions
here my code.

Code:
Public Class Form1

    Private Enum Tokypes
        None = 0
        Digit = 1
        Sysmbol = 2
    End Enum

    'Private Expression As String = "8 * 2 + (10+5)" 'Works fine on this expression.
    Private Expression As String = "8 * 2 + 1" ' VB Crys on this one why

    Private Pos As Integer = 0
    Dim sToken As String = vbNullString
    Dim sTokType As Tokypes

    Private Function isDelim(ByVal c As Char) As Boolean
        If (("+-/*%^=()".IndexOf(c) <> -1)) Then
            Return True
        End If
        Return False
    End Function

    Private Sub GetTokens()
        sToken = vbNullString
        sTokType = Tokypes.None

        If (Pos = Expression.Length) Then
            sToken = vbNullString
            sTokType = Tokypes.None
            Return
        End If

        'Skip white
        While (Pos < Expression.Length) And Char.IsWhiteSpace(Expression(Pos))
            Pos += 1
        End While
        '
        If isDelim(Expression(Pos)) Then
            sToken = sToken & Expression(Pos)
            Pos += 1
            'Token Type.
            sTokType = Tokypes.Sysmbol
        ElseIf Char.IsDigit(Expression(Pos)) Then
            'Thowing error here - Index was outside the bounds of the array.
            While Char.IsDigit((Expression(Pos)))
                sToken = sToken & Expression(Pos)
                Pos += 1
            End While
            If Pos = Expression.Length Then Return
            'Token Type.
            sTokType = Tokypes.Digit
        End If

    End Sub

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

        GetTokens()

        While sTokType <> Tokypes.None
            MsgBox(sToken)
            GetTokens()
        End While

    End Sub
End Class
If you run the code with this expression eveything is fine "8 * 2 + (10+5)"
But if you run it with this you get an out of range error. 8 * 2 + 1
I don't see why cos the first expression has more length than the second.