User Input

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:

• Public sub Add(c As Char) - adds the given character to the current value
• Public function GetValue() As String - returns the current value

Implement the class NumericInput that:

• Inherits TextInput
• Overrides the Add method so that each non-numeric character is ignored

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())