DateAdd("d", -1.0 * DatePart("d", Today), Today)

DateAdd("D", -1.0 * DatePart("D", Today) + 1, Today)

DateAdd("D", -1.0 * DatePart("D", Today) + 1, DateAdd("m", -1, Today))

 public static double ToDouble(DateTime what)
 {
  return BitConverter.ToDouble(BitConverter.GetBytes(what.Ticks), 0);
 }

 public static DateTime ToDateTime(double what)
 {
  return new DateTime(BitConverter.ToInt64(BitConverter.GetBytes(what), 0));
 }

 string myTime = DateTime.Now.ToString("yyyy.MM.dd HH:mm:ss:ffff");
 Console.WriteLine(myTime);

public struct SystemTime
{
 public ushort Year;
 public ushort Month;
 public ushort DayOfWeek;
 public ushort Day;
 public ushort Hour;
 public ushort Minute;
 public ushort Second;
 public ushort Millisecond;
};

[DllImport("kernel32.dll", EntryPoint = "GetSystemTime", SetLastError = true)]
public extern static void Win32GetSystemTime(ref SystemTime st);

[DllImport("kernel32.dll", EntryPoint = "SetSystemTime", SetLastError = true)]
public extern static bool Win32SetSystemTime(ref SystemTime st);

....

public static void Test()
{
 SystemTime newTime = new SystemTime();
 newTime.Year = (ushort)2005;
 newTime.Month = (ushort)12;
 newTime.Day = (ushort)2;
 newTime.Hour = (ushort)12; //UTC time (if you are in UTC+2 zone then you'll put here: time - 2h)
 newTime.Minute = (ushort)42;
 newTime.Second = (ushort)11;
 Win32SetSystemTime(ref newTime);
}

=System.DateTime.ParseExact(Parameters!lic_period_start_date.Value,"dd/MM/yyyy",System.Globalization.DateTimeFormatInfo.InvariantInfo).ToString("yyyyMMdd")

module ActiveRecord
  module ConnectionAdapters
    class ColumnWithIdentity
      def cast_to_time(value)
        return value if value.is_a?(Time) or value.is_a?(DateTime)
        time_array = ParseDate.parsedate(value)
        time_array[0] ||= 2000
        time_array[1] ||= 1
        time_array[2] ||= 1
        Time.send(Base.default_timezone, *time_array) rescue DateTime.new(*time_array[0..5]) rescue nil
      end
      def cast_to_datetime(value)
        if value.is_a?(Time) or value.is_a?(DateTime)
          if value.year != 0 and value.month != 0 and value.day != 0
            return value
          else
            return Time.mktime(2000, 1, 1, value.hour, value.min, value.sec) rescue nil
          end
        end
        return cast_to_time(value) if value.is_a?(Date) or value.is_a?(String) rescue nil
        value
      end
    end
  end
end

import time

class datetime(object):
    def __init__(self, *argv):
        self.t = time.struct_time(argv+(0,)*(9-len(argv)))    # append to length 9 
    def __getattr__(self, name):
        try:
            i = ['year', 'month', 'day', 'hour', 'minute', 'second', 'weekday'].index(name)
            return self.t[i]
        except:
            return getattr(self.t, name)
    def __len__(self): return len(self.t)
    def __getitem__(self, key): return self.t[key]
    def __repr__(self): return repr(self.t)
    def now(self=None):
        return datetime(*time.localtime())
    now = staticmethod(now)
    def strftime(self, fmt="%Y-%m-%d %H:%M:%S"):
        return time.strftime(fmt, self.t)

# here it works like datetime.datetime()
>>> t = datetime.now()
>>> t.year, t.month, t.day
(2006, 3, 13)
>>> t.hour, t.minute, t.second
(23, 3, 28)

# but also works like localtime()
>>> t
(2006, 3, 13, 23, 3, 28, 0, 72, -1)
>>> t.tm_year, t[0]
(2006, 2006)
>>> mktime(t)
1142265808.0

# good default for strftime (= ctime)
>>> t.strftime()
'2006-03-13 23:03:28'

>>> import datetime
>>> now = datetime.datetime(2003, 8, 4, 12, 30, 45)
>>> print now
2003-08-04 12:30:45
>>> print repr(now)
datetime.datetime(2003,8,4,12,30,45)
>>> print type(now)
<type 'instance'>
>>> print now.year, now.month, now.day
2003 8 4
>>> print now.hour, now.minute, now.second
12 30 45

datetime.datetime(2004,1,1).now() # work for any version

datetime.datetime.now() # python 2.3+

    def now(self=None):
        "Return the current date and time as a datetime."
        now = t.localtime()
        return datetime(now[0],now[1],now[2],now[3],now[4],now[5])
    now = staticmethod(now)