#region 得到一周的周一和周日的日期        /// <summary>         /// 计算本周的周一日期         /// </summary>         /// <returns></returns>         public static DateTime GetMondayDate()        {            return GetMondayDate(DateTime.Now);        }        /// <summary>         /// 计算本周周日的日期         /// </summary>         /// <returns></returns>         public static DateTime GetSundayDate()        {            return GetSundayDate(DateTime.Now);        }        /// <summary>         /// 计算某日起始日期（礼拜一的日期）         /// </summary>         /// <param name="someDate">该周中任意一天</param>         /// <returns>返回礼拜一日期，后面的具体时、分、秒和传入值相等</returns>         public static DateTime GetMondayDate(DateTime someDate)        {            int i = someDate.DayOfWeek - DayOfWeek.Monday;            if (i == -1) i = 6;// i值 > = 0 ，因为枚举原因，Sunday排在最前，此时Sunday-Monday=-1，必须+7=6。             TimeSpan ts = new TimeSpan(i, 0, 0, 0);            return someDate.Subtract(ts);        }        /// <summary>         /// 计算某日结束日期（礼拜日的日期）         /// </summary>         /// <param name="someDate">该周中任意一天</param>         /// <returns>返回礼拜日日期，后面的具体时、分、秒和传入值相等</returns>         public static DateTime GetSundayDate(DateTime someDate)        {            int i = someDate.DayOfWeek - DayOfWeek.Sunday;            if (i != 0) i = 7 - i;// 因为枚举原因，Sunday排在最前，相减间隔要被7减。             TimeSpan ts = new TimeSpan(i, 0, 0, 0);            return someDate.Add(ts);        }#endregion

DateTime dt = DateTime.Now;  //当前时间DateTime startWeek = dt.AddDays(1 - Convert.ToInt32(dt.DayOfWeek.ToString("d")));  //本周周一DateTime endWeek = startWeek.AddDays(6);  //本周周日DateTime startMonth = dt.AddDays(1 - dt.Day);  //本月月初DateTime endMonth = startMonth.AddMonths(1).AddDays(-1);  //本月月末//DateTime endMonth = startMonth.AddDays((dt.AddMonths(1) - dt).Days - 1);  //本月月末DateTime startQuarter = dt.AddMonths(0 - (dt.Month - 1) % 3).AddDays(1 - dt.Day);  //本季度初DateTime endQuarter = startQuarter.AddMonths(3).AddDays(-1);  //本季度末DateTime startYear = new DateTime(dt.Year, 1, 1);  //本年年初DateTime endYear = new DateTime(dt.Year, 12, 31);  //本年年末