ASP.NET C#如何获取当月或上个月的第一天和最后一天

////获取当月第一天与最后一天
//DateTime DateNow = DateTime.Now;
//DateTime DateBegin = new DateTime(DateNow.Year, DateNow.Month, 1);
//DateTime DateEnd = DateBegin.AddMonths(1).AddDays(-1);

//获取上个月第一天与最后一天
DateTime DateNow = DateTime.Now.AddMonths(-1);
DateTime DateBegin = new DateTime(DateNow.Year, DateNow.Month, 1);
DateTime DateEnd = DateBegin.AddMonths(1).AddDays(-1);