周、月、季度開始結束時間

             string  nowtime = System.DateTime.Now.ToShortDateString();

            //上周時間
            int n = (int)DateTime.Now.DayOfWeek;
          string  startDate = DateTime.Now.AddDays(-7 - n).ToString("yyyy-MM-dd");//上周第一天
          string  endDate = DateTime.Now.AddDays(-n).ToString("yyyy-MM-dd");//上周最後一天

          //上個月時間
          string startTime = GetFirstDayOfMonth(DateTime.Now.AddMonths(-1)).ToString("yyyy-MM-dd");//第一天
          string endTime = GetLastDayOfMonth(DateTime.Now.AddMonths(-1)).ToString("yyyy-MM-dd"); //最後一天

            //計算季度時間
          int month = DateTime.Now.Month;
          string year=DateTime.Now.Year.ToString();
          string a="" ; string b="";
         if (month > 0 && month < 4)
          {
              a="-01-01";
              b= "-03-31";
          }
         if (month > 3 && month < 7)
          {
             a="-04-01";
            b="-06-30";
          }
         if (month > 6 && month < 10)
          {
             a= "-07-01";
             b= "-09-30";
          }
         if (month > 9 && month < 13)
          {
             a= "-10-01";
             b= "-12-31";
          }
            string seasonStime=year+a;
            string seasonEtime = year+b;