Swift

//: 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