.net中获取周一、月初、月末、年初、年末

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