C# 关于获取周，月，年时间大全

           DateTime now = DateTime.Now;

            DayOfWeek dayOfWeek = now.DayOfWeek;
            int daysWeek = dayOfWeek == DayOfWeek.Sunday ?  : (int)dayOfWeek;
            //本周第一天(此结果是周一，如果想要结果是周日的，不用+1)
            DateTime thisWeekFirstDay = now.AddDays(-daysWeek + );
            Console.WriteLine(thisWeekFirstDay);

            //本月第一天
            DateTime thisMonthFirstDay = now.AddDays(-now.Day + );
            Console.WriteLine(thisMonthFirstDay);

            //本年第一天
            DateTime thisYearFirstDay = now.AddMonths(-now.Month + ).AddDays(-now.Day + );
            Console.WriteLine(thisYearFirstDay);

            //上周第一天(此结果是周一，如果想要结果是周日的，不用+1)
            DateTime lastWeekFrstDay = now.AddDays(-daysWeek -  + );
            Console.WriteLine(lastWeekFrstDay);

            //上周最后一天
            DateTime lastWeekLastdDay = now.AddDays(-daysWeek);
            Console.WriteLine(lastWeekLastdDay);

            //上月第一天
            DateTime lastMonthFirstday = now.AddMonths(-).AddDays(-now.Day + );
            Console.WriteLine(lastWeekLastdDay);

            //上月最后一天
            DateTime lastMonthLastday = now.AddDays(-now.Day);
            Console.WriteLine(lastMonthLastday);

            //上年第一天
            DateTime lastYearFirstDay = now.AddYears(-).AddMonths(-now.Month + ).AddDays(-now.Day + );
            Console.WriteLine(lastYearFirstDay);

            //上年最后一天
            DateTime lastYearLastDay = now.AddMonths(-now.Month + ).AddDays(-now.Day);
            Console.WriteLine(lastYearLastDay);

            Console.ReadLine();

结果如图所示：