Private Sub Worksheet_Change(ByVal Target As Range)
If Not Intersect(Range("B21:O21"), Target) Is Nothing Then
Application.EnableEvents = False
'MsgBox "Quantité obligatoire dans la ligne Normal !" <--- effacer (') pour activer l'affichage du message
For Each cel In Selection
If cel.Row = 21 Then cel.Value = IIf(cel.Value = "", 0, cel.Value)
Next
Application.EnableEvents = True
End If
End Sub