C# DateTime.Now 昨天日期 / 如何設定 datetime 初始值 

資料來源:http://www.cnblogs.com/mzoylee/archive/2009/11/25/1610782.html

http://www.programmer-club.com.tw/ShowSameTitleN/csharp/1614.html

DateTime DTToday = new DateTime(DateTime.Now.Year, DateTime.Now.Month, DateTime.Now.Day, 0, 0, 0, 0);

DateTime DTYesterday = DateTime.Now.AddDays(-1);//DTToday.AddDays(-1);