a)
datetime t1 = new datetime(2008,5,3);
datetime t2 = new datetime(2004,2,22);
timespan span = ( t1>t2 ? t1-t2 : t2-t1);
console.writeline(span.totaldays);

b)
public void DateDiff()
{
DateTime startDate = new DateTime.Parse("11/12/2008");
DateTime endDate = new DateTime.Parse("11/12/2009");

if (endDate > startDate)
TimeSpan span endDate.Subtract(startDate); Console.WriteLine(span);
}