How to accumulate the sum in VB? - vb.net

Question

Dim index As Integer
Dim choice As String
Dim total As Integer
total = 0
index = NumericUpDown1.Value
Dim arr(4) As Integer
arr(0) = 10
arr(1) = 5
arr(2) = 21
arr(3) = 33
If index > 0 Then
choice = (Combobox1.SelectedItem.ToString + " x " + NumericUpDown1.Value.ToString)
ListBox1.Items.Add(choice)
CheckedListBox1.Items.Add(choice)
total += arr(Combobox1.SelectedIndex) * index
TotalLabel.Text = total.ToString()
Else
MsgBox("error.")
End If
I can calculate the total of single choice, but fail to accumulate to sum.
What's wrong of the code?
Current Situation:
Step 1:
choose arr(0), index = 2
total = 20
Step 2:
choose arr(2), index = 1
total = 21
Correct Situation:
Step 1:
choose arr(0), index = 2
total = 20
Step 2:
choose arr(2), index = 1
total = 41

Answer 1

You'll need a either a global variable or a class with a public variable. You should create a Transaction class to store the data about the transaction and probably a Product class to store the data about the product. What you put in it is up to you, but I'd start out with something like this:
Public Class Transaction
Private _productsList As List(of Product)
Private _transationNumber As Integer
'...more stuff...
'you'll want to remember what products are in your "cart" for the transaction
Public Property ProductsList As List(of Product)
'your get/set accessors
End Property
Public Property TransactionNumber As Integer
'your get/set accessors
End Property
Public Property TotalTransactionCost() As Double
Get
'this will sum of the prices of all of the products you have stored in your
'list of products for this transaction
Return _productsList.Sum(product => product.Price)
End Get
End Property
Public Sub New()
'...constructor stuff
End Sub
Public Sub AddProductToTransaction(byval product)
_productsList.Add(product)
End Sub
End Class
Public Class Product
Private _price As Double
Private _productName As String
Private _UPC As String
Public Property Price() As Double
'your get/set accessors
End Property
Public Property ProductName() As String
'your get/set accessors
End Property
Public UPC As String () As String
'your get/set accessors
End Property
Public Sub New()
'constructor stuff
End Sub
End Class
These are a couple class shells to get you started. If you're serious about making a product, this is a step in the right direction. If you're going to write code, write it the right way.
If you're just looking for a quick and dirty solution, you can declare a global variable and just keep a running sum. Just don't forget to clear it out before you start a new transaction.
You'll want to do something like:
Private TransactionCost As Double in your form outside of all your methods.
Again, I would recommend the first way of going about things. You'll need at least those two classes and they'll definitely be more fleshed out for a real product.
I hope this helps and answers your question. If it does, hit me with an upvote and accept the answer. Welcome to SO.