tracking changes in an array

[medicenpringles]

First of all, i would like to thank the MVPs for helping me so much in my last few questions. and with that out of the way, here's my question:

I have a form with 2 check boxes, Small Cheese and Regular Cheese. When the check boxes are clicked it adds or subtracts the correct amount to/from the global total, as shown here:

Private Sub chkSmallCheese_CheckedChanged(ByVal sender As Object, _
ByVal e As System.EventArgs) Handles chkSmallCheese.CheckedChanged

    If chkSmallCheese.CheckState = CheckState.Unchecked Then
        Globals.OrderTotal -= Prices.prcAddChs_sm
        Me.lblOrderTotal.Text = Format(Globals.OrderTotal, "c")
    ElseIf chkSmallCheese.CheckState = CheckState.Checked Then
        Globals.OrderTotal += Prices.prcAddChs_sm
        Me.lblOrderTotal.Text = Format(Globals.OrderTotal, "c")
    End If

End Sub

but my problem is, i need to add 2 more global variables: AdditionCount (an integer), and Addition() (a string array), for addition later to a listbox.

Private Sub chkSmallCheese_CheckedChanged(ByVal sender As Object, _
ByVal e As System.EventArgs) Handles chkSmallCheese.CheckedChanged

    If chkSmallCheese.CheckState = CheckState.Unchecked Then
        [b]Globals.AdditionCount -= 1[/b]
        Globals.OrderTotal -= Prices.prcAddChs_sm
        Me.lblOrderTotal.Text = Format(Globals.OrderTotal, "c")
    ElseIf chkSmallCheese.CheckState = CheckState.Checked Then
        [b]Globals.AdditionCount -= 1[/b]
        Globals.OrderTotal += Prices.prcAddChs_sm
        Me.lblOrderTotal.Text = Format(Globals.OrderTotal, "c")
    End If

    [b]Globals.Additions(Globals.AdditionCount) = "Small Cheese"[/b]

End Sub

but now when i click the checkbox, i get a NullReferenceException, highlighting the line 'Globals.Additions(Globals.AdditionCount) = "Small Cheese"'. I could understand this error if the procedure made the array -1, or nothing, but this doesn't make sense.

any help?

Main Language: Visual Basic .NET
Development Enviroment: Visual Studio .NET 2003

 

[earthandfire]

Arrays are 0 based, therefore the final element is Count - 1


Hope this helps.

 

[RiverGuy]

In your explanation, you say you have named the array Addition. In your code, you have Additions. Did you add an "s" by mistake?

 

[medicenpringles]

Additions is the name of the array. sry about that.

Main Language: Visual Basic .NET
Development Enviroment: Visual Studio .NET 2003

 

[RiverGuy]

You need to size your array. Personally, I would opt to make a collection class. You can use .Add, .Remove, and .Item to work with it. You can also add custom functions such as .Total.

But regardless, if you want to use the array, it seems there is no benefit to have your .AdditionCount variable, since it appears to mirrior the length of your array. Instead of setting .AdditionCount, you can just do a Redim Preserve Global.Additions(Global.Additions.Length +/- 2) and use the .Length property - 1 to get your count.

 

[chiph]

Yup. ArrayLists have many advantages over ordinary arrays.

Chip H.


____________________________________________________________________
If you want to get the best response to a question, please read FAQ222-2244 first

 

[medicenpringles]

well thank you i'll try that.

Main Language: Visual Basic .NET
Development Enviroment: Visual Studio .NET 2003

 

[chrissie1]

could somebody explain me the difference between arraylists and collections and why we need so much of the same. Or are they really that different

Christiaan Baes
Belgium

I just like this --> [Wiggle] [Wiggle]