vérification si une année et bissextile

Private Sub CommandButton1_Click()
If DateSerial(TextBox1, 2, 29) + 1 = DateSerial(TextBox1, 3, 1) Then
    MsgBox "Année Bisextile", vbInformation
        Else
    MsgBox "Année Non Bisextile", vbCritical
End If
End Sub

Function IsBisextile(madate As Date) As Boolean
IsBisextile = Day(DateSerial(Year(madate), 3, 0)) = 29
End Function

Private Sub CommandButton1_Click()
If DateSerial(TextBox1, 2, 29) + 1 = DateSerial(TextBox1, 3, 1) Then
    MsgBox "Année Bisextile", vbInformation
        Else
    MsgBox "Année Non Bisextile", vbCritical
End If
End Sub

Private Sub CommandButton1_Click()[B]
If TextBox1 = "" Then MsgBox "Veuillez entrer une année SVP...": TextBox1.SetFocus: Exit Sub
If Not IsNumeric(TextBox1) Then
MsgBox "Année non valide"
    With TextBox1
        .Value = ""
        .SetFocus
    End With
Exit Sub
End If[/B]
If DateSerial(TextBox1, 2, 29) + 1 = DateSerial(TextBox1, 3, 1) Then
    MsgBox "Année Bisextile", vbInformation
        Else
    MsgBox "Année Non Bisextile", vbCritical
End If
End Sub

If [B]CLng[/B](TextBox1) < 1900