&tag(CSharp/日付と時刻);
DateTime d = new DateTime(2014, 9, 9);
d.ToShortDateString() # => 2014/09/10
DateTime t1 = DateTime.Parse("2011/02/24 03:30");
DateTime t2 = DateTime.Parse("2011/08/11 12:23");
TimeSpan span = t2 - t1;
Debug.WriteLine(span.TotalDays);
int lastDay = DateTime.DaysInMonth(2011, 9);