Note: From my experience in teaching novice programmers, Playgrounds are not as powerful for beginners as they are for experienced programmers. Simply showing how a variable works in the Swift playground doesn’t help a beginner understand the need for a Floating point variable versus an Integer variable. The need becomes obvious when you show an app that can remember your last scroll position in the Facebook news feed. For beginners, the “why” question can only be answered with a working example: an iPhone app.