good old arrays

[anhn]

Try this:

Option Explicit

Private Type Student
  strName As String
  intMark As Integer
End Type

Dim Students() As Student

Private Sub cmdAddRecord_Click()
    Dim iMark As Long
    Dim sName As String
    Dim i As Long
    
    sName = Trim(txtStudentName.Text)
    If sName = "" Then
        MsgBox "student name cannot be blank. Please re-enter it"
        Exit Sub
    End If

    iMark = Val(txtStudentMark.Text)
    If iMark < 0 Then
        MsgBox "student mark cannot be less than zero. Please re-enter it"
        Exit Sub
    ElseIf iMark > 100 Then
        MsgBox "student mark cannot be greater than 100. Please re-enter it"
        Exit Sub
    End If
    
    If (Not Students) = -1 Then '-- Students() array was not initialized
        i = 1
    Else
        i = UBound(Students) + 1
    End If
    ReDim Preserve Students(1 To i)
    
    Students(i).strName = sName
    Students(i).intMark = iMark
       
    lstNames.AddItem sName
    lstMarks.AddItem iMark

End Sub