'-------------------------------------------------------------------------------------------

'                                                BOOKMANAGER CLASS

'This module contains the capability to compute sales totals, sales tax, and amount due for
'each transaction. It also maintains a running total of daily sales figures (actual # of books sold 
'and total amt of $$ collected, and total sales tax collected.

'The class has three properties: Price, Quantity, & Taxrate
'
'-------------------------------------------------------------------------------------------
Public Class BookManager

    Private bookPrice As Decimal           'property for the price of the book
    Private myquantity As Integer        'property for quantity of books purchased
    Private storeTaxRate As Decimal       'the tax rate is passed from btnCalculate_click
    Private totalTax As Decimal           'hold the actual formatted value of the tax



#Region "Properties"
    '---here we manage the price they will send/get from our class
    '   ***Properties are PUBLIC by default so you can leave off "Public" when declaring them***
    ''' <summary>
    ''' Sets or gets the Price of the book as a decimal
    ''' </summary>
    Property Price() As Decimal
        Get
            Return bookPrice
        End Get
        Set(ByVal value As Decimal)
            bookPrice = value
        End Set
    End Property
    '---here we manage the quantity they will send/get from our class
    ''' <summary>
    ''' Sets or gets the quantity of the books sold as an integer.
    ''' </summary>
    
    Property Quantity() As Integer
        Get
            Return myquantity
        End Get
        Set(ByVal Value As Integer)
            If Value >= 0 Then
                myquantity = Value
            End If
        End Set
    End Property

    ''' <summary>
    ''' Sets or gets the store tax rate as a decimal
    ''' </summary>
   
    Property TaxRate() As Decimal
        Get
            Return storeTaxRate

        End Get
        Set(ByVal Value As Decimal)
            storeTaxRate = Value
        End Set
    End Property

#End Region


#Region "Methods"

    ''' <summary>
    ''' This method computes the amount of sales tax as a decimal.
    ''' </summary>
    
    Public Function ComputeTax() As Decimal

        '---calculate the sales tax based on the numbers they pass to us
        Dim Tax As Decimal
        Tax = FormatNumber(quantity * bookPrice * taxRate, 2)

        totalTax = Tax    'save this so I can use it again in the ComputeTotalSale Function

        Return Tax              'send this back to the calling procedure(btnCalculate_click)

    End Function

    ''' <summary>
    ''' This method computes the total sale using the price, quantity, and salestax properties and returns a decimal.
    ''' </summary>
    Public Function ComputeTotalSale() As Decimal
        '---now compute the total sale
        Dim Total As Decimal
        Total = FormatNumber((bookPrice * Quantity) + totalTax, 2)
        Return Total

        '---you can also do it like this if you want:
        'Return (bookPrice * quantity) + totalTax

    End Function

    ''' <summary>
    ''' This method computes the sub total of the sale using the price and quantity properties and returns a decimal.
    ''' </summary>

    Public Function ComputeSubTotal() As Decimal

        Dim SubTotal As Decimal
        SubTotal = FormatNumber(Quantity * bookPrice, 2)

        Return SubTotal
    End Function


#End Region
End Class

***************Here I use the class to manage running totals in the store


Private Sub btnCalculate_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnCalculate.Click
        If txtQuantity.Text = "" Or txtPrice.Text = "" Then
            MsgBox("Please complete the form....", MsgBoxStyle.Exclamation, "Book Store Message")
            Exit Sub
        End If
        '---they are ready to check out

        '---assign stuff from text boxes to MybookStore so it can do its thing
        Try

            '---pass my class the stuff in the text box
            MyBookStore.Price = txtPrice.Text
            MyBookStore.Quantity = txtQuantity.Text
            MyBookStore.TaxRate = SALESTAXRATE

            '---compute this purchase
            txtTax.Text = MyBookStore.ComputeTax.ToString
            txtsubTotal.Text = MyBookStore.ComputeSubTotal.ToString
            txtTotalDue.Text = MyBookStore.ComputeTotalSale.ToString

            '---update daily totals
            dailyNumSales += CInt(txtQuantity.Text)
            dailySales += CDec(txtTotalDue.Text)
            dailySalesTax += CDec(txtTax.Text)

            '---now put totals in the labels
            lblGrandNumSales.Text = dailyNumSales.ToString
            lblGrandTotalSales.Text = FormatNumber(dailySales.ToString, 2)
            lblGrandTotalTax.Text = FormatNumber(dailySalesTax.ToString, 2)

        Catch
            MsgBox("An error occured while completing this transaction." & Err.Description, MsgBoxStyle.Critical, "Broken Book Transaction")
            PrepareMyForm()
        End Try

    End Sub