Boucle for next renvoyant 0

Private Sub CommandButton1_Click()
Dim o As Object
Dim a As Integer
Dim y As Integer
Dim z As Integer

a = 1
Set o = Sheets("Base")
For y = 1 To o.Range("IV1").End(xlToLeft).Column
    For z = 2 To o.Range("A65536").End(xlUp).Row
        If o.Cells(z, y) = "" Then o.Cells(z, y) = 0
        Sheets("RANGEMENT").Range("A" & a) = o.Cells(z, y)
        a = a + 1
    Next z
Next y
End Sub

Private Sub CommandButton1_Click()
Dim a%, y%,z%
a = 1
With Sheets("Base")
For y = 1 To .Range("IV1").End(xlToLeft).Column
    For z = 2 To .Range("A65536").End(xlUp).Row
        If .Cells(z, y) = "" Then .Cells(z, y) = 0
        Sheets("RANGEMENT").Range("A" & a) = .Cells(z, y)
        a = a + 1
    Next z
Next y
End With
End Sub

Private Sub CommandButton1_Click()
Dim j&, v&, h&, Plg As Range
    With Worksheets("BASE")
        v = .Cells(2 ^ 16, 1).End(xlUp).Row - 1
        If v Then
            h = .Cells(1, 2 ^ 8).End(xlToLeft).Column
            With .Cells(2, 1).Resize(v, h)
                If .Cells.Count > 1 Then
                    On Error Resume Next
                    .SpecialCells(xlCellTypeBlanks).Value = 0
                    On Error GoTo 0
                End If
                Set Plg = Worksheets("RANGEMENT").Cells(1, 1).Resize(v)
                For j = 1 To h
                    Plg.Offset(v * (j - 1)) = .Columns(j).Value
                Next
            End With
        End If
    End With
End Sub