/// <summary>
        /// 获取指定日期，在为一年中为第几周
        /// </summary>
        /// <param name="dt">指定时间</param>
        /// <reutrn>返回第几周</reutrn>
        public static int GetWeekOfYear(DateTime dt)
        {

            System.Globalization.GregorianCalendar gc = new System.Globalization.GregorianCalendar();
            int weekOfYear = gc.GetWeekOfYear(dt, System.Globalization.CalendarWeekRule.FirstDay, DayOfWeek.Monday);
            return weekOfYear;
        }


        public static int WeekOfMonth(DateTime day, int WeekStart)
        {
            //WeekStart
            //1表示 周一至周日 为一周
            //2表示 周日至周六 为一周
            DateTime FirstofMonth;
            FirstofMonth = Convert.ToDateTime(day.Date.Year + "-" + day.Date.Month + "-" + 1);

            int i = (int)FirstofMonth.Date.DayOfWeek;
            if (i == 0)
            {
                i = 7;
            }

            if (WeekStart == 1)
            {
                return (day.Date.Day + i - 2) / 7 + 1;
            }
            if (WeekStart == 2)
            {
                return (day.Date.Day + i - 1) / 7;

            }
            return 0;
            //错误返回值0
        }

获取此实例所表示的日期为该月中的第几天

      DateTime.Today.Day