Private morseCodeDictionary As New Dictionary(Of Char, String) From {{"a"c, ".-"},
                                                                 {"b"c, "-..."},
                                                                 {"c"c, "-.-."}}

Private Sub inputTextBox_TextChanged(sender As Object, e As EventArgs) Handles inputTextBox.TextChanged
outputTextBox.Text = String.Join(" ",
                                 inputTextBox.Text.
                                              ToLower().
                                              Select(Function(ch) morseCodeDictionary(ch)))