Maze module

Option Explicit
Option Base 0

Private Z() As Integer
Private tmpCell(3) As Cell
Private Cells As New Collection

Public Sub Generate(ByVal Width As Integer, ByVal Height As Integer)
    Dim neighbors() As New Cell
    Dim current As New Cell
    Dim i As Integer
    Dim j As Integer


    Set tmpCell(0) = CreateCell(0, 1)
    Set tmpCell(1) = CreateCell(0, -1)
    Set tmpCell(2) = CreateCell(1, 0)
    Set tmpCell(3) = CreateCell(-1, 0)



    initStack


    current.x = 1
    current.y = 1

    Cells.Add current

    ReDim Z(Width - 1, Height - 1)

    Randomize

    For i = 0 To Width - 1
        For j = 0 To Height - 1
            Z(i, j) = 1
        Next
    Next i

    While Cells.Count > 0
        Z(current.x, current.y) = 0
        neighbors = GetValidNeighbors(current, Width, Height)
        'REM neighbors(x) is never actually nothing, even if said to be so
        'doing the "neighbors(x) is nothing" compaison magically creates a class
        If neighbors(0) Is Nothing And neighbors(1) Is Nothing And neighbors(2) Is Nothing And neighbors(3) Is Nothing Then
            Set current = Pop()
        Else
            Push current
            Set current = GetRnd(neighbors)
        End If
    Wend
End Sub

Private Function GetValidNeighbors(centerTile As Cell, ByVal Width As Integer, ByVal Height As Integer) As Cell()
    Dim Count As Integer
    Dim i As Integer
    Dim toCheck As New Cell
    Dim validNeighbors(3) As Cell

    For i = 0 To 3
        Set toCheck = New Cell
        toCheck.x = centerTile.x + tmpCell(i).x
        toCheck.y = centerTile.y + tmpCell(i).y

        'Explicitely setting nothing also does not work
        Set validNeighbors(i) = Nothing

        If (toCheck.x Mod 2 = 1 Or toCheck.y Mod 2 = 1) And IsInside(toCheck, Width, Height) Then
            If Z(toCheck.x, toCheck.y) = 1 And HasThreeWallsIntact(toCheck, Width, Height) Then
                Set validNeighbors(Count) = New Cell
                validNeighbors(Count).x = toCheck.x
                validNeighbors(Count).y = toCheck.y
                Count = Count + 1
            End If
        End If
    Next

    GetValidNeighbors = validNeighbors
End Function

Private Function HasThreeWallsIntact(toCheck As Cell, ByVal w As Integer, ByVal h As Integer)
    Dim Count As Integer
    Dim i As Integer
    Dim neighborToCheck As New Cell

    Count = 0

    For i = 0 To 3
        Set neighborToCheck = New Cell
        neighborToCheck.x = toCheck.x + tmpCell(i).x
        neighborToCheck.y = toCheck.y + tmpCell(i).y

        If IsInside(neighborToCheck, w, h) Then
            If Z(neighborToCheck.x, neighborToCheck.y) = 0 Then
                Count = Count + 1
            End If
        End If
    Next
    HasThreeWallsIntact = Count
End Function

Private Function IsInside(c As Cell, ByVal w As Integer, ByVal h As Integer) As Boolean
    IsInside = (c.x >= 0 And c.y >= 0 And c.x < w And c.y < h)
End Function

''CELL''
Private Function CreateCell(x As Integer, y As Integer)
    Dim a As New Cell
    a.x = x
    a.y = y
    Set CreateCell = a
End Function

''STACK''
Private Sub initStack()
    Set Cells = New Collection
End Sub

Private Sub Push(newItem As Variant)
    With Cells
        .Add newItem
    End With
End Sub

Public Function Pop() As Variant
    With Cells
        If .Count > 0 Then
            Set Pop = .Item(.Count)
            .Remove .Count
        End If
    End With
End Function

''MISC''
Private Function IsVarArrayEmpty(anArray As Variant)
    Dim i As Integer

    On Error Resume Next
    i = UBound(anArray, 1)
    If Err.Number = 0 And i <> -1 Then
        IsVarArrayEmpty = False
    Else
        IsVarArrayEmpty = True
    End If

End Function

Private Function GetRnd(arr)
    Dim a
    Set a = Nothing

    While a Is Nothing
        Set a = arr(Rnd * UBound(arr))
    Wend

    Set GetRnd = a
End Function

Public Sub Test()
    Call Generate(10, 10)
End Sub