I wrote a little app that calculates the number of days between two dates.
It's very simple and not complete for example it does not handle landscape orientation BUT it took me ~5 minutes to write.
OK that's a bit of a lie. I must have spent at least 10 minutes reading and testing alternative solutions using NSCalendar & NSDateComponents. It just didn't do exactly what I wanted so I computed the days myself. I feel there is a better solution but this one works!
It still tickles me how easy it is to write IOS apps.