Data Structure Problems

[Rue]

Code im using is

Public Structure pupil
Dim name As String
Dim age As Int16
Dim id As Int16
Dim pupilClass As String
End Structure

Public Structure pupilList
Dim list() As pupil
Dim count
End Structure

Dim ListData As New pupilList()

then to try and access the pupil name im using

MsgBox(ListData.list(ListData.count).age)

it give me a error saying that the last line is not set to a instance of the object?

any help would be great on how i can update/desplay the name,age etc , cheers!

[Borry]

Just an idea .... maybe you need to set the count to int16 as well ?

[<ABX]

First of all, since pupilList.List is an array it is zero based so

MsgBox(ListData.list(ListData.count).age)

would refer to a item that is not in the array

Second, The way you set it up you would have to do the following before adding anything

'to get it to work the way you you have it setup now..
 
        ReDim ListData.list(0)
        ListData.count = 1
 
        ListData.list(0) = New pupil
 
        MsgBox(ListData.list(ListData.count - 1).age)

The way I would do it...

Option Explicit On 
 
Public Class cPupilCollection
    Inherits System.Collections.CollectionBase
 
    ' Restricts to cPupil types, items that can be added to the collection.
    Public Sub Add(ByVal acPupil As cPupil)
        ' Invokes Add method of the List object to add a cPupil.
        List.Add(acPupil)
    End Sub
 
    Public Sub Remove(ByVal index As Integer)
        ' Check to see if there is a cPupil at the supplied index.
        If index > Count - 1 Or index < 0 Then
            ' If no cPupil exists, a messagebox is shown and the operation is 
            ' cancelled.
            System.Windows.Forms.MessageBox.Show("Index not valid!")
        Else
            ' Invokes the RemoveAt method of the List object.
            List.RemoveAt(index)
        End If
    End Sub
 
    ' This line declares the Item property as ReadOnly, and 
    ' declares that it will return a cPupil object.
    Public ReadOnly Property Item(ByVal index As Integer) As cPupil
        Get
            ' The appropriate item is retrieved from the List object and 
            ' explicitly cast to the cPupil type, then returned to the 
            ' caller.
            Return CType(List.Item(index), cPupil)
        End Get
    End Property
 
End Class

Option Explicit On 
 
Public Class cPupil
 
    Private m_strName As String
    Private m_sAge As Short ' Short = Int16
    Private m_sID As Short
    Private m_strPupilClass As String
 
    Public Property PupilName() As String
        Get
            Return m_strName
        End Get
        Set(ByVal Value As String)
            m_strName = Value
        End Set
    End Property
 
    Public Property Age() As Short
        Get
            Return m_sAge
        End Get
        Set(ByVal Value As Short)
            m_sAge = Value
        End Set
    End Property
 
    Public Property ID() As Short
        Get
            Return m_sID
        End Get
        Set(ByVal Value As Short)
            m_sID = Value
        End Set
    End Property
 
    Public Property PupilClass() As String
        Get
            Return m_strPupilClass
        End Get
        Set(ByVal Value As String)
            m_strPupilClass = Value
        End Set
    End Property
 
End Class

'usage:
 
 
Dim Test as New PupilCollection
 
Dim  NewPupil as New Pupil
 
NewPupil.PupilName = "Bob"
NewPupil.Age = 10
 
Test.Add(NewPupil)