Sub zumye()
Dim Cell As Range
Dim Message as String
Application.ScreenUpdating = False
For Each Cell In Range("i19:y300")
If Not IsEmpty(Cell) And Len(Cell) = 1 Then
Message = Message & Cell.Address(0, 0) & Chr(13)
End If
Next Cell
MsgBox "Les cellules suivantes ne contiennent qu'une lettre: " _
& Chr(13) & Chr(13) & Message, vbCritical, "Message d'alerte"
Application.ScreenUpdating = True
End Sub