Sub Test()
Dim I As Long
Dim Txt As String
Txt = ""
I = 1
Colonne_1 = AtoZ(Txt)
Colonne_2 = AtoZ(Colonne_1)
Colonne_3 = AtoZ(Colonne_2)
End Sub
Function AtoZ(ByVal Txt As String, Optional ByVal inx As Long = 0) As String
Txt = Space(inx + 1) & Txt
For I = Len(Txt) - inx To 1 Step -1
If Trim(Mid(Txt, I, 1)) = "" Then Mid(Txt, I, 1) = "A": AtoZ = Txt: Exit Function
If Trim(Mid(Txt, I, 1)) = "Z" Then Mid(Txt, I, 1) = "A": AtoZ = AtoZ(Txt, inx + 1): Exit Function
Mid(Txt, I, 1) = Chr(Asc(Mid(Txt, I, 1)) + 1): AtoZ = Trim(Txt): Exit Function
Next
End Function