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Swift基础加强
创建一个playGround，然后看一下代码，跟着打，别复制粘贴。
1 // Playground - noun: a place where people can play 2 3 import UIKit 4 5 // HelloWorld 6 var str = "Hello, playground" 7 8 // 常量可以改变值 9 var myVariable = 42 10 myVariable = 50 11 let myConstant = 42 12 13 // 指定数据类型 14 let floatNumber:Float = 4 15 16 // 使用强制转换 17 let lable = "the lable is " 18 let width = 94 19 let labelwidth = lable + String(width) 20 21 // 使用双引号中的\来转换 22 let apples = 3 23 let oranges = 5 24 let appleSummary = "i have \(apples) apples" 25 let orangeSummary = "i have \(oranges) oranges" 26 27 // 自动识别数据类型加斜杠转换 28 let somebody = "Alice" 29 let age = 23.5 30 let hellosomebody = "\(somebody) is \(age)" 31 32 // 数组的初始化以及赋值 33 var shoppingList = ["Alice", "Dylan"] 34 shoppingList[1] = "Petit Alice" 35 36 // 字典的初始化以及赋值 37 var occupations = [ 38 39 "male" : "Alice", 40 "female" : "Dylan" 41 ] 42 occupations["male"] = "Alice.Petit" 43 44 // 初始化一个空的数组或者字典 45 let emptyArray = [String]() 46 let emptyDictionary = [String:Float]() 47 48 // 初始化一个自动识别类型的字典或者数组 49 let emptyArray_auto = [] 50 let emptyDictionary_auto = [:] 51 52 // 控制流 不能省略大括号 53 let individualScores = [75, 42, 103, 87, 12] 54 var teamScore = 0 55 for score in individualScores { 56 if score > 50 { 57 teamScore += 3 58 } else { 59 teamScore += 1 60 } 61 } 62 teamScore 63 64 // 写到这里 突然发现 变量名称直接打出去 就能打印了 65 let emptyA = ["key": "value"] 66 emptyA 67 68 // 在if条件中 条件必须是bool表达式 输如一个直接score会出错的 看好了 是必须是表达式 69 70 // 使用let来标记 71 var optionalString: String? = "Hello" 72 optionalString == nil 73 74 var optionalName: String? = "John Appleseed" 75 var getting = "Hello" 76 optionalName = nil 77 78 if let name = optionalName { 79 getting = "hello, \(name)" 80 } else { 81 getting = "hello, Alice" 82 } 83 84 // switch 85 let vegetable = "red pepper" 86 switch vegetable { 87 case "celery": 88 let vegetableComment = "add some