IMEI Number validation using VB.NET

Private Sub TextBox1_TextChanged(ByVal sender As System.Object, ByVal e As System.EventArgs)
            If TextBox1.Text.Length = 15 Then
                          Dim IMEI As String = TextBox1.Text 
                          Dim cnt As Integer = 0 
                          Dim nw As String = ??
                   For Each c As Char In
                          IMEIcnt += 1
                            If cnt Mod 2 <> 0 Then
                                  nw += c
                            Else
                                 Dim d As Integer = Integer.Parse(c) * 2nw += d.ToString()
                            End If
                  Next
Dim tot As Integer = 0 
For Each ch As Char In nw.Remove(nw.Length ? 1, 1)
          tot +=Integer.Parse(ch)
Next
Dim chDigit As Integer = 10 ? (tot Mod 10)  
         If chDigit = Integer.Parse(IMEI(IMEI.Length ? 1)) Then
                  MsgBox(?Valid?) 
          Else
                  MsgBox(?Invalid?) 
         End If
    End If
End Sub