Performing Calculations with Modules in Visual Basic - vb.net

Question

I am writing a program for my Visual Basic class that is supposed to be able to calculate the final total price for items selected from one list box and added to another. 2 of the items have sales tax that must be added into the final price. The program also has a Module that is supposed to be used to keep record of all taxes and is used to do all tax-related functions.
Here is the most current code.
Option Strict On
Public Class Form1
Private Sub btnAdd_Click(ByVal sender As Object, ByVal e As EventArgs) Handles btnAdd.Click
If (txtQuantity.Text = "") Then
MessageBox.Show("Please enter a quantity for the item you selected")
ElseIf Not Integer.TryParse(txtQuantity.Text, CInt(txtQuantity.Text)) Then
MessageBox.Show("The quantity entered is not numeric. Please add a numeric quantity.")
Exit Sub
Else
lstPurchased.Items.Add(txtQuantity.Text & " " & lstSale.Text)
End If
End Sub
Private Sub btnCalculate_Click(ByVal sender As Object, ByVal e As EventArgs) Handles btnCalculate.Click
Dim int As Integer
Dim total As Double = 0
For i As Integer = 0 To lstPurchased.Items.Count - 1
Dim lst() As String = lstPurchased.Items(i).ToString.Split({CChar(" ")}, 2)
Integer.TryParse(lst(0), int)
total += TaxesModule.SalesTax(int, lst(1))
Next
MessageBox.Show(CStr(FormatCurrency(total)))
End Sub
Private Sub btnClear_Click(ByVal sender As Object, ByVal e As EventArgs) Handles btnClear.Click
lstPurchased.Items.Clear()
txtQuantity.Clear()
End Sub
End Class
And the most recent code for the module
Option Strict On
Module TaxesModule
Private Const DONUT_TAX As Decimal = CDec(0.083)
Private Const RAISIN_TAX As Decimal = CDec(0.02)
Private Const SS_TAX As Decimal = CDec(0.062) ' <-- you are not using this
Public Function SalesTax(ByVal Quantity As Integer, ByVal item As String) As Double
Dim TotalWithSalesTax As Double
If item = "Wheat Bread" Then
TotalWithSalesTax += (Quantity * 1.15)
ElseIf item = "White Bread" Then
TotalWithSalesTax += (Quantity * 1.05)
ElseIf item = "Donuts" Then
TotalWithSalesTax += (Quantity * (0.5 * DONUT_TAX) + (Quantity * 0.5))
ElseIf item = "Raisins" Then
TotalWithSalesTax += (Quantity * (0.25 * RAISIN_TAX) + (Quantity * 0.25))
End If
Return TotalWithSalesTax
End Function
End Module
As the code is written now, the only problem I'm having is that the TotalWithSalesTax for "Raisins" is not calculating correctly. For example, if I select "Raisins" from the list box and add it with a quantity of 1 to the other list box, the total that is displayed in the message box is $0.00.
I'm starting to think the issue is with the following section of code:
For i As Integer = 0 To lstPurchased.Items.Count - 1
Dim lst() As String = lstPurchased.Items(i).ToString.Split({CChar(" ")}, 2)
Because I have tried making changes such as
For i As Integer = 1 ...
And that caused both Donuts and Raisins to give me a total of $0.00 in the message box. So I'm wondering if maybe how the count is set up is not allowing it to go through the entire list, but I don't know how to fix that?
I'm still really new to Visual Basic, and programming in general really and this is my first time working with modules. Can anybody help me figure out what I'm doing wrong, so I can move onto other parts of the program?

Answer 1

I have modified your code, hope this is what you want. Added comment in the code. Note i have removed all Public variables.
Public Class Form1
Private Sub btnAdd_Click(ByVal sender As Object, ByVal e As EventArgs) Handles btnAdd.Click
If (txtQuantity.Text = "") Then
MessageBox.Show("Please enter a quantity for the item you selected")
ElseIf Not Integer.TryParse(txtQuantity.Text, txtQuantity.Text) Then
MessageBox.Show("The quantity entered is not numeric. Please add a numeric quantity.")
Exit Sub
Else
lstPurchased.Items.Add(txtQuantity.Text & " " & lstSale.Text)
End If
End Sub
Private Sub btnCalculate_Click(ByVal sender As Object, ByVal e As EventArgs) Handles btnCalculate.Click
Dim int As Integer
Dim total As Double = 0
'you have to loop through the list to calculate the total
' hope this is what you want
For i As Integer = 0 To lstPurchased.Items.Count - 1
' We split the list item into the quantity and the item name
Dim lst() As String = lstPurchased.Items(i).ToString.Split({CChar(" ")}, 2)
'lst(1) contains the item name
Integer.TryParse(lst(0), int)
total += TaxesModule.SalesTax(int, lst(1))
Next
MessageBox.Show(CStr(FormatCurrency(total)))
End Sub
Private Sub btnClear_Click(ByVal sender As Object, ByVal e As EventArgs) Handles btnClear.Click
lstPurchased.Items.Clear()
txtQuantity.Clear()
End Sub
End Class
The module
Module TaxesModule
Private Const DONUT_TAX As Decimal = CDec(0.083)
Private Const RAISIN_TAX As Decimal = CDec(0.02)
Private Const SS_TAX As Decimal = CDec(0.062) ' <-- you are not using this
Public Function SalesTax(ByVal Quantity As Integer, ByVal item As String) As Double
Dim TotalWithSalesTax As Double
If item = "Wheat Bread" Then
TotalWithSalesTax = (Quantity * 1.15)
ElseIf item = "White Bread" Then
TotalWithSalesTax = (Quantity * 1.05)
ElseIf item = "Donuts" Then
TotalWithSalesTax = (Quantity * (0.5 * DONUT_TAX) + (Quantity * 0.5))
ElseIf item = "Raisins" Then
TotalWithSalesTax = (Quantity * (0.25 * RAISIN_TAX) + (Quantity * 0.25))
End If
Return TotalWithSalesTax
End Function
End Module