Programmation VBA

Private Sub CommandButton1_Click()
'Cells(7, 6) = InputBox("Entrez la maturité de l'obligation")
n = Range("F7").Value
'Cells(9, 6) = InputBox("Entrez la valeur faciale de l'obligation")
F = Range("F9").Value
'Cells(11, 6) = InputBox("Entrez le montant du coupon périodique")
C = Range("F11").Value
'Cells(13, 6) = InputBox("Entrez le taux de rendement actuariel")
R = Range("F13").Value
Sum = 0
For k = 1 To n
    Sum = (C / (1 + R) ^ k) + Sum
Next k
Cells(16, 6) = Sum + (F / (1 + R) ^ n)
End Sub

Private Sub Worksheet_Change(ByVal Target As Range)
If Not Intersect(Target, Range("F13")) Is Nothing Then
For i = 7 To 13 Step 2
If IsEmpty(Cells(i, 6).Value) = True Then MsgBox "Veuillez remplir le champs " & Cells(i, 2).Value: Exit Sub
Next i
n = Range("F7").Value
F = Range("F9").Value
C = Range("F11").Value
R = Range("F13").Value
Sum = 0
For k = 1 To n
Sum = (C / (1 + R) ^ k) + Sum
Next k
Cells(16, 6) = Sum + (F / (1 + R) ^ n)
End If
End Sub