Private Sub btnCalc_Click(sender As Object, e As EventArgs) Handles btnCalc.Click

    Dim intDays As Integer
    Dim decRate As Decimal
    Dim decFinalAmount As Decimal

    Const _cradPenny As Decimal = 0.01D
    Const _cradNickel As Decimal = 0.05D

    If IsNumeric(txtDays.Text) Then
        intDays = Convert.ToInt32(value:=txtDays.Text)

        If intDays >= 10 And intDays <= 22 Then

            If radPenny.Checked = True Then
                decRate = _cradPenny

            ElseIf radNickel.Checked = True Then
                decRate = _cradNickel

            End If

        Else
            MsgBox("Nope, nope. Please enter an amount between 10 and 22.", , "Input Error")
            txtDays.Text = ""
            txtDays.Focus()

        End If

    End If

    decFinalAmount = decRate(intDays - 1) ^ intDays

    lblTotalPay.Text = "Your total pay is " & decFinalAmount.ToString("C")
    lblTotalPay.Visible = True


End Sub

I have decRate declared, with constants that are determined by the radio button selected.
What am I missing?

我声明了DecRate，其中的常量由选中的单选按钮确定。我遗漏了什么？

I am expecting to run the formula:

我希望运行公式：

decFinalAmount = decRate(intDays - 1) ^ intDays

In VB.NET, there is no implicit multiplication for a(b+c), you have to write a*(b+c). If you write x(y), you might be referring to a method named x that you are passing a parameter y to, or it could be an array x that you want the y-th value of.

在VB.NET中，a(b+c)没有隐式乘法，必须写a*(b+c)。如果您编写x(Y)，您可能会引用一个名为x的方法，您将向该方法传递一个参数y，或者它可能是一个您想要其第y个值的数组x。

Also, it is usually a good idea to factor out things like that calculation. You can make sure that that small part of the program functions correctly on its own, and it makes it re-usable without having to type out the formula again.

此外，将这样的计算计算出来通常是一个好主意。您可以确保程序的这一小部分自行正确运行，并使其可重复使用，而不必再次键入公式。

There are some other parts of VB that you might like to investigate, so here is my take on what you might be able to learn more from:

您可能会想要研究一下VB的其他一些部分，所以下面是我对您可能能够从中学到更多东西的看法：

Function CompoundInterestFinalAmount(initial As Decimal, rate As Decimal, paymentPeriodBase As Double, paymentPeriods As Double) As Decimal
    Return CDec(initial * ((1 + rate / paymentPeriodBase) ^ (paymentPeriodBase * paymentPeriods)))
End Function

Private Sub btnCalc_Click(sender As Object, e As EventArgs) Handles btnCalc.Click

    Const CRADPENNY As Decimal = 0.01D
    Const CRADNICKEL As Decimal = 0.05D

    ' INTERESTRATE is the actual number, so 5% interest is 0.05D.
    Const INTERESTRATE As Decimal = 0.05D

    Const DAYSMIN As Integer = 10
    Const DAYSMAX As Integer = 22

    Dim days As Integer

    If Int32.TryParse(txtDays.Text, days) Then

        If days >= DAYSMIN AndAlso days <= DAYSMAX Then

            Dim initialAmount As Decimal

            Select Case True
                Case radPenny.Checked
                    initialAmount = CRADPENNY
                Case radNickel.Checked
                    initialAmount = CRADNICKEL
                Case Else
                    MsgBox("Please choose pennies or nickels.")
                    Exit Sub
            End Select

            Dim finalAmount = CompoundInterestFinalAmount(initialAmount, INTERESTRATE, 1, days)

            lblTotalPay.Text = $"Your total pay is {finalAmount:C}."
            lblTotalPay.Visible = True

        End If

    Else
        MsgBox($"Nope, nope. Please enter an amount between {DAYSMIN} and {DAYSMAX}.", MsgBoxStyle.Information, "Input Error")
        txtDays.Clear()
        txtDays.Focus()

    End If

End Sub

Thanks dr.null - I got the decRate setup as an array and my error was no more!

谢谢，Null博士-我得到了作为数组的DecRate设置，我的错误再也没有了！