If you are looking for a DateDiff function in C# like in VB or SQL Server, there is none. However here are some options to perform date operations in .Net via C#.
You can subtract two DateTime objects which returns a TimeSpan object. Here is an example:
//To get the amount of days between two dates. DateTime date1 = new DateTime(2007,1,1); DateTime date2 = DateTime.Today; int daysDiff = ((TimeSpan) (date2 - date1)).Days;
Write you own DateDiff function. Of course somebody already has. Just copy and paste.
For VB fans, you can reference the Microsoft.VisualBasic dll and access the VB DateDiff function directly. See the example on this page.