รบกวนผู้รู้อธิบายโคดนี้หน่อยนะครับ Private Sub show_check()

 Private Sub show_check()
        If rbt_cash.Checked = True Then
            lbl_saledate.Text = Date.Today.ToLongDateString
            lbl_salepay.Text = Date.Today.ToLongDateString
            auto_billpay()
            TextBox2.Text = billID
        ElseIf rbt_cash.Checked = False Then
            Dim i As Integer
            Dim i1 As Integer
            If Date.Today.Month = 12 Then
                i = Date.DaysInMonth(Date.Today.Year + 1, 1)
                i1 = i - Date.Today.Day + 15
                lbl_salepay.Text = Date.Today.AddDays(i1).ToLongDateString
                lbl_saledate.Text = Date.Today.ToLongDateString
            Else
                i = Date.DaysInMonth(Date.Today.Year, Date.Today.Month)
                i1 = i - Date.Today.Day + 15
                lbl_salepay.Text = Date.Today.AddDays(i1).ToLongDateString
                lbl_saledate.Text = Date.Today.ToLongDateString
            End If
            TextBox2.Text = "ไม่มีเลขที่ใบเสร็จ"
        End If
        auto_saleID()
    End Sub