How do add days to a date in ObjC?

Question

I want to find the future date after adding a number of days to another date.

So if I have this:

 NSDateComponents *pastDate = [[NSDateComponents alloc] init];
        [pastDate setMonth:12];
        [pastDate setDay:23];
        [pastDate setYear:2011];

and want to add 90 days to find the future date. What method should I be looking at? I got creating another variable. I'm interested in what method. Thanks.