Public Class DisplayListBox

    Private Sub CalculateButton_Click(sender As System.Object, e As System.EventArgs) Handles CalculateButton.Click
        Dim TextBoxPrincipalDouble As Double
        Dim TextBoxInterestDouble As Double
        Dim TextBoxInt As Integer
        Try
            TextBoxPrincipalDouble = CDbl(PrincipalTextBox.Text)
            TextBoxInterestDouble = CDbl(InterestTextBox.Text)
            TextBoxInt = CInt(YearTextBox.Text)
        Catch
            MessageBox.Show("Please enter valid numbers.", "Entry Error")
        End Try
        If (TextBoxInterestDouble >= 0 And TextBoxInterestDouble < 1) Then
            Dim DepositClass As Deposit = New Deposit(TextBoxPrincipalDouble, TextBoxInterestDouble)
            If AccountTypeCheckBox.Checked = True Then
                Dim val As CompoundInterestDeposit = New CompoundInterestDeposit(TextBoxPrincipalDouble, TextBoxInterestDouble)
                val.CompoundBalance(Year)
            Else
                Dim val As Deposit = New Deposit(TextBoxPrincipalDouble, TextBoxInterestDouble)
                val.TotalBalance(Year)
            End If
        End If
    End Sub
End Class


Public Class Deposit
    Public Interest As Double
    Public Deposit As Double
    Public Balance As Double

    Public Sub New()
        Interest = 0
        Deposit = 0
    End Sub
    Public Sub New(ByVal Int As Integer, ByVal Dep As Integer)
        Interest = Int
        Deposit = Dep
    End Sub

    Function TotalBalance(ByVal Year As Integer) As Integer
        Balance = Deposit * (1 + (Year * Interest))
        Return Balance
    End Function
End Class

Public Class CompoundInterestDeposit
    Inherits Deposit
    Public Sub New(ByVal Interest As Integer, ByVal Deposit As Integer)
        Interest = 0
        Deposit = 0
    End Sub
    Function CompoundBalance(ByVal Year As Integer) As Integer
        Balance = Deposit * (1 + Interest) ^ Year
        Return Balance
    End Function

End Class