打印输出

println("hello,world")

末尾不需要加分号

定义变量用var，常量用let

var myVariable = 42
let myConstant = 42

变量和常量的类型应该和我们想要的类型一致，编译器可以帮助我们推断类型，我们也可以显示指定类型

let explicitDouble: Double = 70

显示转换类型

let width = 94
let widthLable = lable + String(width)

在字符串中打印数值，在要格式化的数值前加”()”

let apples = 3
let oranges = 5
let appleSummary = "I have \(apples) apples."
let fruitSummary = "I have \(apples + oranges) pieces of fruit."

创建数组和字典

//数组
var shoppingList = ["catfish","water","tulips","blue paint"]
shoppingList[1] = "bottle of water"
//字典
 var occupations = [
     "Malcolm": "Captain","Kaylee": "Mechanic",]
occupations["Jayne"] = "Public Relations"

创建空数组和字典

let emptyArray = String[]()
let emptyDictionary = Dictionary<String,Float>()