Visual Basic GUI Input Validation - vb.net

Question

I took an entry level computer programming class this past term and I'm having problems with my final project. I have to design a program in visual basic GUI that asks the player to accurately guess a number between 1-100 within a limited number of guesses.
My first form asks the user to set the number of guesses allowed. It has one textbox and an "enter" button, among other buttons that I've gotten to work.
I'm trying to get code to work that will validate the input on the guesses allowed. Specifically, I want a message box to pop up if the player enters letters or special characters instead of numbers, or enters a number less than zero, or greater than twenty. Here's what I have:
Public Class Noofguesses
Shared maxguesscnt As Integer
Private Sub Numberofguesses_TextChanged(sender As Object, e As EventArgs) Handles Numberofguesses.TextChanged
End Sub
Private Sub Quit_Click(sender As Object, e As EventArgs) Handles Quit.Click
End
End Sub
Private Sub Button2_Click(sender As Object, e As EventArgs) Handles Button2.Click
Form3.Show()
End Sub
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
If Val(Numberofguesses) > 20 Then MsgBox("Number of Guesses Cannot Exceed 20")
If Val(Numberofguesses) < 0 Then MsgBox("Number of Guesses Must Be Greater Than 0")
If Not IsNumeric(Numberofguesses) Then MsgBox("Entry Cannot be Letters or Characters")
Me.Close()
Form2.Show()
End Sub
End Class
What am I doing wrong? Please let me know.
Thanks

Answer 1

I would generally suggest using a NumericUpDown rather than a TextBox, in which case no validation is required. As this is an assignment though, I'm guessing that validating a TextBox is a requirement. In that case, you should use Integer.TryParse to validate a String, i.e. the Text of the TextBox and convert it if it is valid. You can then test the converted value to make sure that it isn't less than zero, etc. I'm not going to write the code for you, given that this is homework, but that should be enough for you to do it yourself or, if you feel you must, find examples online.