//: Playground - noun: a place where people can play import UIKit var str = "Hello, playground" // 数值类型转换
let three = 3
let PI = Double(three) + 0.1415926 // 两个类型不相同的数值不能进行基础运算,所以进行数值类型转换 // 类型别名(typealias)
typealias NSInterger = Int
var number : NSInterger = 10
var count = NSInterger.max