Random number guessing game VB - vb.net

Question

OBJECTIVE:
This is a guessing game. The program is to generate a random number between 1 and 500. The user is to guess the number.
The form should include a START button, a listbox to hold all valid guesses, and a label displaying the answer.
Upon clicking the START button, the user will enter a number in response to an InputBox().
If the user’s guess is invalid (not numeric, not a whole number, out of range), display an appropriate message.
If the guess is valid but is not the correct number (high or low), display an appropriate message.
image high quess dialog boximage low quess dialog box
Every time the user guesses a valid numeric guess within range, add the guess to the listbox on the form. Allow the guesses to be shown in multiple columns in the listbox.
If the user successfully guesses the number, display an appropriate message. Include how many guesses they took. Count only valid (in range, integral) numeric guesses as a guess.
Allow the user to quit the game by entering Quit in response to the input box. If the user gives up, tell them the correct number
Important: Display the random number in a label immediately after generating it so that I (and you) know what the number is while I am (and you are) testing it. You can obviously take it out if you really want to play the game.
Private Sub btnStart_Click(sender As Object, e As EventArgs) Handles btnStart.Click
'Declare Variables
Dim strGuess As String
Dim random As New Random
Dim answer As Integer
'Start with empty Boxes
lstGuesses.Items.Clear()
answer = random.Next(1, 500)
lblAnswer.Text = CStr(answer)
Do
Try
strGuess = InputBox("Enter a numeric integer between 1 and 500. , Enter 'quit' to Quit.", "Guessing Game")
lstGuesses.Items.Add(strGuess)
If strGuess = CStr("quit") Then
MessageBox.Show("The number was " & answer & ". Click Start Game to play again.")
Exit Do
End If
If CInt(strGuess) < CInt(1) Then
MessageBox.Show("Invalid Guess. Enter an Integer Number between 1 and 500!")
End If
If CInt(strGuess) > CInt(500) Then
MessageBox.Show("Invalid Guess. Enter an Integer Number between 1 and 500!")
End If
If CInt(strGuess) = CInt(answer) Then
MessageBox.Show("Got it! You guessed " & lstGuesses.Items.Add(strGuess) & " times!")
End If
If CInt(strGuess) > CInt(answer) And CInt(strGuess) <= CInt(500) Then
MessageBox.Show("Guess is High")
End If
If CInt(strGuess) < CInt(answer) And CInt(strGuess) >= CInt(1) Then
MessageBox.Show("Guess is Low")
End If
If lstGuesses.Items.Contains("quit") = True Then
MessageBox.Show("The number was " & answer & ". Click Start Game to play again.")
End If
Catch ex As InvalidCastException
'Make user guess
MessageBox.Show("Invlid Guess. Enter a numeric integer between 1 and 500!")
End Try
Loop While CInt(strGuess) <> answer
End Sub
MY PROBLEM:
I have been trying everything and this is the best i have made yet. This homework is due in 4 hours so any help will be appreciated.
I am suppose to type the word "quit" to end the game. But also give an error message when something other than letters are typed. Every time I type a letter and press enter, it gives the warning that i set but then it crashes. It is not supposed to crash. It says the crash is from:
Loop While CInt(strGuess) <> answer
and the problem is because of an InvalidCastException and says convertion from string to type integer is not valid. I tried doing TRYPARSE but still the same problem. Can anyone tell me how to let me type the word "quit" into the box so that it quits the game, but doesn't make it crash.

Answer 1

Maybe this is not the best way but i think it will help.
What you need to do is Make a new if statement at the top just after the user entered something in the inputbox.
If IsNumeric(strGuess) Or strGuess = CStr("quit") Then
Else
MessageBox.Show("Only Numbers")
GoTo Line1
End If
And here you check "If IsNumeric(strGuess) Or strGuess = CStr("quit") Then"
if yes do nothing
If No show a msgbox and use a goto "GoTo Line1" "so above your do you add Line1:"
If somebody types something like "a" he will go to line1 "so start the do" and the user needs to enter something new in the inputbox.
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
'Declare Variables
Dim strGuess As String
Dim random As New Random
Dim answer As Integer
'Start with empty Boxes
lstGuesses.Items.Clear()
answer = random.Next(1, 500)
lblAnswer.Text = CStr(answer)
Line1:
Do
Try
strGuess = InputBox("Enter a numeric integer between 1 and 500. , Enter 'quit' to Quit.", "Guessing Game")
lstGuesses.Items.Add(strGuess)
If IsNumeric(strGuess) Or strGuess = CStr("quit") Then
Else
MessageBox.Show("Only Numbers")
GoTo Line1
End If
If strGuess = CStr("quit") Then
MessageBox.Show("The number was " & answer & ". Click Start Game to play again.")
Exit Do
End If
If CInt(strGuess) < CInt(1) Then
MessageBox.Show("Invalid Guess. Enter an Integer Number between 1 and 500!")
End If
If CInt(strGuess) > CInt(500) Then
MessageBox.Show("Invalid Guess. Enter an Integer Number between 1 and 500!")
End If
If CInt(strGuess) = CInt(answer) Then
MessageBox.Show("Got it! You guessed " & lstGuesses.Items.Add(strGuess) & " times!")
End If
If CInt(strGuess) > CInt(answer) And CInt(strGuess) <= CInt(500) Then
MessageBox.Show("Guess is High")
End If
If CInt(strGuess) < CInt(answer) And CInt(strGuess) >= CInt(1) Then
MessageBox.Show("Guess is Low")
End If
If lstGuesses.Items.Contains("quit") = True Then
MessageBox.Show("The number was " & answer & ". Click Start Game to play again.")
End If
Catch ex As InvalidCastException
'Make user guess
MessageBox.Show("Invlid Guess. Enter a numeric integer between 1 and 500!")
End Try
Loop While CInt(strGuess) <> answer
End Sub