User interface contains two types of user input controls: TextInput, which accepts all characters and NumericInput, which accepts only digits.

Implement the class TextInput that contains:

Implement the class NumericInput that:

For example, the following code should output "10":

Dim input As TextInput = New NumericInput()
input.Add(CChar("1"))
input.Add(CChar("a"))
input.Add(CChar("0"))
Console.WriteLine(input.GetValue())