Linked List in VB ! 2

Category:

Miscellaneous

Type:

Snippets

Difficulty:

Intermediate

Author:

Anonymous

Version Compatibility: Visual Basic 6, Visual Basic 5

More information:

'''Please read the introduction before jump in to the code '''========================================================= ''' ************************** ''' Linked List Program in VB ''' By M.Ganesh Sathya Narayanan, ''' Spearhead Technologies,Coimbatore ''' ************************** ''' ************************** ''' How it Is possible! ''' =================== ''' In C/C++/VC++ Linked List perform through pointers. But VB has ''' no pointers.Then How it is possible! ''' Through OBJECTS . Objects can be refered as a pointer ''' If you set ''' Set obj=New Person ''' Now VB allocates the memory for obj ''' Now obj holds the reference(i.e.Pointers) to the Person(class) ''' ************************** ''' *************************************** ''' How to free the allocated memory ''' ================================ ''' Just set ''' set obj=Nothing ''' ************************************** ''' **** ''' NOTE ''' **** ''' ************************************** ''' How to compare two objects ''' ************************************** ''' To Compare TWO Objects don't use =(equal operator) ''' Bcos objects having reference to the class(Ex:set obj=New Person) ''' Then what is the solution ''' Just use Is keyword ''' Eg: ''' *** ''' if obj Is Person ''' ''' if obj Is Nothing ''' ''' ************************************** ''' ************************************** ''' You can download the whole linklist program at ''' http://www.chipware.cjb.net ''' or mail me at tidelganesh@hotmail.com(TIDELGANESH@HOTMAIL.COM) ''' subject as LinkedList ''' I will send as attachment ''' **************************************

Instructions: Copy the declarations and code below and paste directly into your VB project.

Declarations:
''Create a Class Module LinkList '''''' Link List Class ''' File Name: LinkList.cls Public Item As String 'To store our Items Public pNext As LinkList 'It holds next node pointer !'(i.e;Object) Private Sub Class_Initialize() Set pNext = Nothing End Sub Private Sub Class_Terminate() Set pNext = Nothing End Sub ''General_Declaration of the form ================================= Dim sItem As String Dim temp As LinkList Dim Head As LinkList Dim First As LinkList 'Alwyas Points Starting of the List Dim i as integer

Code:

'''Insert in to a node
Private Sub InsertNode()

Do While Not UCase(sItem) = "END"
    i = i + 1

sItem = InputBox("Enter the Item(Type 'End' to Finish)", , "Item" & i)
    sItem = Trim(sItem)
        If Head Is Nothing Then
            Set temp = New LinkList
            temp.Item = sItem
            Set Head = temp
            Set First = Head
        Else
            Set temp = New LinkList
            temp.Item = sItem
            Set Head.pNext = temp
            Set Head = temp
        End If
        If UCase(sItem) = "END" Then
        Set Head.pNext = Nothing
        End If
    Loop
    
   Call DisPlayNode
End Sub
'''''''---------------------------------------------------
'Delete a Particular Node

Private Sub DeleteNode()
Dim sDelStr As String
Dim d As LinkList
Dim holdPrev As LinkList 'Hold Previous location while deleting
Set temp = Nothing
Set p = Nothing
Set holPrev = Nothing
Set d = First

If d Is Nothing Then
'        Text1.Text = "No Items In the List
' ! Insert Something 'before Delete !"
Debug.print "No Items In the List"
        Exit Sub
    End If
    
sDelStr = InputBox("Enter the Item Name to Delete")
sDelStr = UCase(Trim(sDelStr))

Do While Not d Is Head
  
  
        If UCase(d.Item) = sDel Then
        If holPrev Is Nothing Then
                Set First = d.pNext
                Call cmdPrint_Click
                Exit Sub
        End If
            Set d = holPrev
            Set d.pNext = temp.pNext
            Call DisPlayNode
            Exit Sub
            
            Else
                Set holPrev = d
                Set temp = d.pNext
                Set d = d.pNext
        End If
    Loop
     
     Set p = Nothing
End Sub

''''''-------------------------------------
'Display all Nodes in the list

Private Sub DisPlayNode()
Dim p As LinkList
Set p = First
If p Is Nothing Then
debug.print= ""
Debug.Pring = "No Items in the List"
Exit Sub
End If
Do While Not p Is Head
'Text1.Text = Text1.Text & p.Item & "--->"
        Debug.Print  p.Item & "--->"
        Set p = p.pNext
Loop
Set p = Nothing
End Sub
''''-----------------------

'''''
Cleanup all allocated memory

Private sub free()
Set temp = Nothing
Set Head = Nothing
Set First = Nothing
Set holdPrev = Nothing
end sub