//: Playground - noun: a place where people can play

import UIKit

var str = "Hello, playground"

//var 声明变量 很像JavaScript

var myVariable = 42;

myVariable = 50;

//let 声明常量 JavaScript 的新标准也是用let吧 C++里的const

let myConstant = 42;

let implicitInteger = 70;

let implicitDouble = 70.0;

//显式指定一个常量的类型 用 ： （冒号）

let explicitDouble : Double = 70;

let explicitFloat : Float = 4;

let label = "The width is"

let width = 94;

//值永远不会被隐式转换为其他类型。如果你需要把一个值转换成其他类型,请显式转换。 如下，必须把 width 强转为 String才能 和label(String 类型)拼接

let widthLabel = label + String(width);

let apples = 3;

let oranges = 5;

//有一种更简单的把值转换成字符串的方法:把值写到括号中,并且在括号之前写一个反斜杠

let applesSummary = "I have \(apples) apples.";

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

let mingboHeight = 18.00

let mingbo = " \(mingboHeight)" + " mingbo";

//使用方括号 [] 来创建数组和字典,并使用下标或者键(key)来访问元素。最后一个元素后面允许有个逗号。再也不用担心多写一个逗号了

var shoppingList = ["catfish", "water", "tulips", "blue paint"];

shoppingList[1] = "bottle of water";

var occupations = [

    "Malcolm":"Captain",

    "Kaylee":"Mechanic",

];

occupations["Jayne"] = "Public Relations";

//要创建一个空数组或者字典,使用初始化语法。

let emptyArray = [String]();

let emptyDictionary = [String :Float]();

//如果类型信息可以被推断出来,你可以用 [] 和 [:] 来创建空数组和空字典——就像你声明变量或者给函数传参 数的时候一样。

shoppingList = [];

occupations = [:];