Program ktory liczy ksiazki

  Dim Title As String
        Dim Books As Integer
        Dim Costperbook As Single
        Dim Totalcost As Decimal
        Dim Voucher As String
        Dim DiscountRate As Single
        Dim Discount As Decimal
        Dim DiscountVoucher As Integer

        Costperbook = 15.99
        DiscountVoucher = 25

        txtTitle.Text = InputBox("Please Enter your book name")
        txtBooks.Text = InputBox("Please Enter Amount you'd like to buy")
        txtCostperbook.Text = InputBox("Please Enter the cost of the book", & 15.99 &)
        txtVoucher.Text = InputBox("Please Say yes or no")

        txtTitle.Text = Title
        Books = txtBooks.Text
        txtTotalcost.Text = Totalcost
        
        
        Books = InputBox("You cannot order less than 1 book or  more than 80", "Enter Amount")
        Do While Books <= 1 Or Books >= 80
            MsgBox("Your entry is out of range please choose amount from 1-80")
            Books = InputBox("You cannot order less than 1 book or  more than 80", "Enter Amount")
        Loop
        
        Voucher = InputBox("Please enter Y or y if you are using a voucher if not Enter N or n if you are not using voucher", "Pick an answear")
        Do Until Voucher = "Y" Or Voucher = "y" Or Voucher = "N" Or Voucher "n"
            MsgBox("Voucher incorrect, Please try again")
            Voucher = ("Please try again")

        Loop

        If Books >= 5 Or Books <= 10 Then
            DiscountRate = 0.05
        Elseif Books >= 11 Or Books <= 50 Then
            DiscountRate = 0.075
        Elseif Books >= 51 Then
            DiscountRate = 0.1
        End If
        
        If Voucher = "Y" Or Voucher = "y" Then
            Discount = ((Costperbook * Books) * DiscountRate)
            Totalcost = Totalcost - Discount - DiscountVoucher

        End If

        If Voucher = "N" Or Voucher = "n" Then
            Totalcost = Books * Costperbook
        End If
        
        
    End Sub

    Private Sub btnClear_Click(sender As Object, e As EventArgs) Handles btnClear.Click
        txtBooks.Clear()
        txtCostperbook.Clear()
        txtVoucher.Clear()
        txtTotalcost.Clear()