Untitled

Imports System.Text.RegularExpressions
Imports System.IO
Module Module1
    Sub Main()
        Dim stextbox As String = "trees"
        Dim sletters As String = Regex.Replace("ABCDEFGHIJKLMNOPQRSTUVWXYZ", "[" & stextbox & "]", "", RegexOptions.IgnoreCase)
        Dim cletters As Char() = sletters.ToCharArray()
        For Each c In cletters
            Console.WriteLine("%{0}%", c)
        Next c
    End Sub
End Module