C# DateTime evaluation problem

Question

So I'm trying to figure out what I'm doing wrong with this logic. It seems straightforward and my breakpoints indicate that the evaulation in the 'if' statement is resolving as True, but sum.ppStart et al aren't getting 14 days added to them.

It's probably something simple, but any help would be appreciated.

//Determine the start/end days of each week of the pay period and retrieve a list of those entries

DateTime[] weeks = timeTools.calcPP(0);
DateTime today = DateTime.Now.Date;

if (today > weeks[3])
{
  weeks[0].AddDays(14);
  weeks[3].AddDays(14);
  weeks[4].AddDays(14);
}

sum.ppStart = weeks[0];
sum.ppEnd = weeks[3];
sum.payDate = weeks[4];

Answer 1

AddDays returns a new instance of DateTime, the existing value is not changed, it is an immutable structure. When using the function, capture the result

DateTime myDate = ...
myDate = myDate.AddDays(14);

Answer 2

That is because you're not using the result of the AddDays method. The signature is

 public DateTime AddDays(double days) 

or so (see link). You need to do this:

weeks[0] = weeks[0].AddDays(14);