Public Class Form1

    Private Sub btnGo_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnGo.Click

        Dim ave As Double
        Dim total As Double  ' acuumulator
        Dim count As Integer ' counter
        Dim numQuizzes As Integer
        Dim isConverted As Boolean
        Dim isConverted2 As Boolean

        ' convert # quizzes
        isConverted = Integer.TryParse(txtNumQuiz.Text, numQuizzes)

        ' check # quizzes
        If isConverted AndAlso numQuizzes > 0 Then
            For count = 1 To numQuizzes
                ' ask for current score
                Dim currentScoreString As String
                Dim currentScore As Double
                currentScoreString = InputBox("What is your score on quiz " & count & "?")

                ' convert and validate
                isConverted2 = Double.TryParse(currentScoreString, currentScore)
                If isConverted2 AndAlso currentScore >= 0 AndAlso currentScore <= 10 Then
                    total = total + currentScore
                Else
                    MsgBox("Please enter a quiz grade between 0 and 10")
                End If
            Next count
            txtTotal.Text = total.ToString("n2")
            ave = total / numQuizzes
            txtAve.Text = ave.ToString("n2")
        Else
            MsgBox("Please enter a number greater than zero")
        End If

    End Sub
End Class