C#獲取當月的第一天最后一天 獲取本周第一天最后一天

　　　　　　　DateTime nowTime = DateTime.Now;
            #region 獲取本周第一天
            //星期一為第一天  
            int weeknow = Convert.ToInt32(nowTime.DayOfWeek);

            //因為是以星期一為第一天，所以要判斷weeknow等於0時，要向前推6天。  
            weeknow = (weeknow == 0 ? (7 - 1) : (weeknow - 1));
            int daydiff = (-1) * weeknow;

            //本周第一天  
            DateTime FirstDay = nowTime.AddDays(daydiff);
            #endregion

            #region 獲取本周最后一天
            //星期天為最后一天  
            int lastWeekDay = Convert.ToInt32(nowTime.DayOfWeek);
            lastWeekDay = lastWeekDay == 0 ? (7 - lastWeekDay) : lastWeekDay;
            int lastWeekDiff = (7 - lastWeekDay);

            //本周最后一天  
            DateTime LastDay = nowTime.AddDays(lastWeekDiff);
            #endregion

            //獲取當前月的第一天
            DateTime d1 = new DateTime(nowTime.Year, nowTime.Month, 1);

            //獲取當前月的最后一天
            DateTime d2 = d1.AddMonths(1).AddDays(-1);

            Console.WriteLine(FirstDay);
            Console.WriteLine(LastDay);
            Console.WriteLine(d1);
            Console.WriteLine(d2);
            Console.Read();