Convert DateTime to Double

Hi experts!

  Im using C# 2008 , WinForm NET 2. I need somethink not very common, but I used to work with date like double and this save me many trouble with date format.

I have DateTime variable and want to get it Double value (to be more clear, I need only date part without time so will truncate only integer part). How to do this ?  I need some think like :

       DateTime dt = DateTime.Now;
           
       double dtDOuble = Convert.ToDouble(dt);

 This produce error &