PersianCalendar pc = new PersianCalendar();

            DateTime thisDate = DateTime.Now;

            int month = pc.GetMonth(thisDate);

​

            if (month<4) PersianSeasson = "بهار";

            else if (month > 3 && month < 7) PersianSeasson = "تابستان";

            else if (month > 6 && month < 10) PersianSeasson = "پاییز";

            else if (month > 9) PersianSeasson = "زمستان";

​

            MessageBox.Show(PersianSeasson);