I need help with my linked list program.

[RGB255]

We started linked lists today at school and I sort of get how the adding code works to add to the list but I don't know how to make code that will "remove" items from the list. Any help on this would be awsome. Thanks.

code:

Private Type NameList     Data As String     Link As Integer End Type   Dim linkvar(100) As NameList Dim First_loca, Spot_loca, Vacant_loca, Vacant_loca_temp As Integer   Private Sub Command3_Click() Vacant_loca_temp = Vacant_loca Vacant_loca = 2 Call Command1_Click Vacant_loca = Vacant_loca_temp End Sub   Private Sub Command4_Click() Form1.Caption = linkvar(1).Data End Sub   Private Sub Form_Load() 'Initialize Linked List   For x = 1 To 99     linkvar(x).Link = x + 1 Next x   'Set last item to null linkvar(100).Link = 0   'Set First_loca and Vacant_loca First_loca = 0   'list empty Vacant_loca = 1  'initial open position End Sub   Private Sub Command1_Click()        'Add to list 'If Vacant_loca_temp > 0 Then '    Vacant_loca = Vacant_loca_temp '    Vacant_loca_temp = 0 'End If 'Update Vacant_loca Postion Spot_loca = Vacant_loca Vacant_loca = linkvar(Spot_loca).Link   'Place input into array linkvar(Spot_loca).Data = Text1 Text1 = "" Text1.SetFocus   'Establish Position in the List Form1.Caption = Spot_loca 'this also sets the links I think 'Check to see if item is First_loca If First_loca = 0 Or linkvar(Spot_loca).Data < linkvar(First_loca).Data Then     linkvar(Spot_loca).Link = First_loca    'Points to what previous First_loca pointed to     First_loca = Spot_loca                'Makes new item First_loca in list Else        'New Item is not the First_loca in the list     Pointer1 = First_loca     pointer2 = linkvar(First_loca).Link     'The two pointers around the position where the new     'item is inserted need to be corrected         'Find the Correct Position in the list     Do Until pointer2 = 0 Or linkvar(Spot_loca).Data < linkvar(pointer2).Data         'loops until the end of the list, or the correct position is found                 Pointer1 = pointer2         pointer2 = linkvar(pointer2).Link         'moves through the list, when the loop stops,         'these two pointers must be adjusted     Loop           linkvar(Pointer1).Link = Spot_loca 'fixing links     linkvar(Spot_loca).Link = pointer2 End If Call Command2_Click End Sub   Private Sub Command2_Click() 'Clear Listbox List1.Clear   'Output the linked list in order 'Current is a local pointer used to move through the list Dim Current As Integer   'Current begins at First_loca Current = First_loca   Do Until Current = 0     List1.AddItem linkvar(Current).Data   'output data     Current = linkvar(Current).Link       'move to next item Loop End Sub

[wtd]

With all due respect, if you're using an array, then you don't have a linked list.

[RGB255]

So how would I go about making a proper linked list?

[rdrake]

If you look at the [WIP] C Whirlwind then you will see an example of a linked list in C. Not sure if that helps, though.

[wtd]

A linked list is formed from nodes. Each node contains a value of some type, and a link to another node.

In a language like C or C++, this will often take the form of a pointer to another node. If the pointer is NULL, then the current node is assumed to be the end of the list.

Other languages may have different ways to represent this boolean logic.

[RGB255]

Okay the code may not be a true linked list but can anyone help me with the code that will allow me to replace an item in the list and then allow me to keep adding to the end of the list?

[wtd]

I hate to harp on this incessantly, but style matters Indenting the contents of your subroutines would make it much easier to trace what is going on.

Of course, more of an MVC approach would help too, with the code to manage a "linked list" kept separate from the code for the UI.

The problem with adding to the end of the list is that your solution is based on an array. The array is of fixed size, and thus cannot grow in the same way a true linked list can.

[RGB255]

Well this is just supposed to be an example to show us the concept so I didn't bother to make it in a dynamic array. The problem is the teacher left us to figure out the code that will allow us to replace an item in the list. The problem I get is that when I try to replace an item everything gets out of order and doesn't work.

[Silent Avenger]

Well linked lists are complicated things so I won't just give you the answer to your problem but I'll give you hints and in this way you'll learn how the linked list works. First of all if if you look how your initial links are set up you'll see a pattern which is that each empty spot points to the next empty spot. So you learn from this that you'll also need to change the link of the spot you're trying to remove. Also if you try running your program a few times you'll notice that if you remove a spot it doesn't really change the order of the list so you'll also have to change the link of the item that pointed to your removed item. With this you should be able to figure out the code that you need to remove an Item.

[RGB255]

Okay thanks for the tips. I'll try them out.

[Silent Avenger]

One other thing to tell you the code that you're going to come up with isn't going to remove the first item so you'll have to do some thinking.

[RGB255]

Thanks it worked!

[Silent Avenger]

You're welcome. See now that you know how it works it makes it a lot easier to figure out the code to remove an item.