yian的专栏

本系列学习教程https://developer.apple.com/library/ios/documentation/Swift/Conceptual/Swift_Programming_Language/GuidedTour.html#//apple_ref/doc/uid/TP40014097-CH2-XID_1

2. Simple values 1) Use let to make a constant andvar to make a variable 2) A constant or variable must have the same type as the value you want to assign to it 3) However, you don’t always have to