日期计算
day   =DateTime.Today;
      取出今天日期,,,怎么算昨天的啊
      谢谢

------解决方案--------------------
DateTime dt = DateTime.Today;
dt = dt.AddDays(-1);
dt.Date
------解决方案--------------------
DateTime dt = DateTime.Today;
Console.WriteLine(dt.AddDays(-1));

------解决方案--------------------
day = DateTime.Today.AddDays(-1);