Linked List: Program code ( visual basic )

Computer Science(9608) notes and Resources

Linked List: A linked list is a data structure that provides links between data items. The data items are in an arranged order in the linked list.

 Implementation of Linked List in Visual basic.

Module Module1

    Dim Itemlist(4) As ListNode

    Dim headpointer, freepointer As Integer

    Dim nextFreeAddress As Integer

    Dim currentPointer, previousPointer As Integer

    Structure ListNode

        Dim name As String

        Dim pointer As Integer

    End Structure

    Sub Main()

        createLinkedList()

        additem("apple")

        additem("orange")

        additem("grapes")

        additem("banana")

        Console.WriteLine(" Printing items of linked list: ")

        Console.WriteLine(Itemlist(headpointer).name)

        Console.WriteLine(Itemlist(Itemlist(headpointer).pointer).name)

        Console.WriteLine(Itemlist(Itemlist(Itemlist(headpointer).pointer).pointer).name)

        Console.WriteLine(Itemlist(Itemlist(Itemlist(Itemlist(headpointer).pointer).pointer).pointer).name)

        Console.WriteLine(" Removing items: ")

        removeitem("orange")

        removeitem("apple")

        Console.WriteLine("  Adding items: ")

        additem("coconut")

        additem("potato")

        Console.WriteLine(" Printing items of linked list: ")

        Console.WriteLine(Itemlist(headpointer).name)

        Console.WriteLine(Itemlist(Itemlist(headpointer).pointer).name)

        Console.WriteLine(Itemlist(Itemlist(Itemlist(headpointer).pointer).pointer).name)

        Console.WriteLine(Itemlist(Itemlist(Itemlist(Itemlist(headpointer).pointer).pointer).pointer).name)

        Console.WriteLine()

        Console.Write(" Type an item be searched: ")

        Dim itemSearch As String

        itemSearch = Console.ReadLine()

        searchItem(itemSearch)

        Console.ReadLine()

    End Sub

    Sub createLinkedList()

        For index = 1 To 4

            Itemlist(index).pointer = index + 1

        Next

        Itemlist(4).pointer = 0

        freepointer = 1

        headpointer = 0

    End Sub

    Sub removeitem(ByVal newItem As String)

        Dim found As Boolean = False

        currentPointer = headpointer

        If Itemlist(currentPointer).name = newItem Then

            headpointer = Itemlist(currentPointer).pointer

            Itemlist(currentPointer).pointer = freepointer

            freepointer = currentPointer

            found = True

        Else

            While currentPointer <> 0 And found = False

                previousPointer = currentPointer

                currentPointer = Itemlist(currentPointer).pointer

                If Itemlist(currentPointer).name = newItem Then

                    Itemlist(previousPointer).pointer = Itemlist(currentPointer).pointer

                    Itemlist(currentPointer).pointer = freepointer

                    freepointer = currentPointer

                    found = True

                End If

            End While

        End If

        If found = False Then

            Console.WriteLine(" Item to be deleted not found in linked list!")

        End If

    End Sub

    Sub searchItem(ByVal newItem As String)

        Dim found As Boolean = False

        currentPointer = headpointer

        While currentPointer <> 0 And found = False

            If Itemlist(currentPointer).name = newItem Then

                Console.WriteLine(newItem & " is found at address: " & CStr(currentPointer) & " and it points to the node at adress: " & CStr(Itemlist(currentPointer).pointer))

                found = True

            End If

            currentPointer = Itemlist(currentPointer).pointer

        End While

        If found = False Then

            Console.WriteLine(" Item not found in linked List! ")

        End If

    End Sub

    Sub additem(ByVal newItem As String)

        If freepointer <> 0 Then

            Itemlist(freepointer).name = newItem

            nextFreeAddress = Itemlist(freepointer).pointer

            currentPointer = headpointer

            While Itemlist(currentPointer).name < newItem And currentPointer <> 0

                previousPointer = currentPointer

                currentPointer = Itemlist(currentPointer).pointer

            End While

            If currentPointer = headpointer Then

                Itemlist(freepointer).pointer = headpointer

                headpointer = freepointer

            Else

                Itemlist(freepointer).pointer = currentPointer

                Itemlist(previousPointer).pointer = freepointer

            End If

            freepointer = nextFreeAddress

        Else

            Console.WriteLine(" There is no free space! ")

        End If

    End Sub

End Module

                                                                                                         - CIE A-LEVEL COMPUTER SCIENCE (  9608 )