swift基础语法(控制流、可选类型、switch、循环、开闭空间)

 1 // Playground - noun: a place where people can play
 2 
 3 import Cocoa
 4 
 5 //控制流
 6 
 7 //Swift的条件语句包括if和switch，循环语句包含for-in、for、while和do-while，循环/判断条件不需要括号，但循环/判断体(body)必需括号：
 8 let individualScores = [75, 43, 103, 87, 12]
 9 var teamScore = 0
10 for score in individualScores {
11     if score > 50 {
12         teamScore += 3
13     }else{
14         teamScore += 1
15     }
16 }
17 
18 //可空类型
19 //结合if和let，可以方便的处理可空变量(nullable variable)。对于空值，需要在类型声明后添加？显示标明该类型可空。
20 var optionalString: String? = "Hello"
21 optionalString = nil
22 
23 var optionalName: String? = "John Applesed"
24 var gretting = "Hello!"
25 if let name = optionalName{
26     gretting = "Hello, \(name)"
27 }
28 
29 //灵活的switch
30 let vegetable = "red pepper"
31 switch vegetable {
32     case "celery":
33         let vegetableComment = "Add som raisins and make ants on a log."
34     case "cucumber","watercress":
35         let vegetableComment = "That would make a good tea sandwich."
36     case let x where x.hasSuffix("pepper"):
37         let vegetableComment = "Is it a spicy \(x)?"
38     default:
39         let vegetableComment = "Everything tastes good in soup."
40 }
41 
42 //其他循环
43 //for-in 除了遍历数组也可以用来遍历字典
44 let interestingNumbers = [
45     "Prime":[2,3,5,7,11,13],
46     "Fibonacci":[1,1,2,3,5,8],
47     "Square":[1,4,9,16,25],
48 ]
49 var largest = 0
50 for(kind, numbers) in interestingNumbers{
51     for number in numbers{
52         if number > largest{
53             largest = number
54         }
55     }
56 }
57 
58 //while循环和do-while循环
59 var n = 2
60 while n < 100 {
61     n = n * 2
62 }
63 n
64 
65 var m = 2
66 do{
67     m = m * 2
68 }while m < 100
69 m
70 
71 
72 //Swift支持传统的for循环，此外也可以通过结合..（生成一个区间）和for-in实现同样的逻辑
73 var firstForLoop = 0
74 for i in 0..3{
75     firstForLoop += i
76 }
77 firstForLoop
78 
79 var secondForLoop = 0
80 for var i = 0; i < 3; ++i{
81     secondForLoop += 1
82 }
83 secondForLoop
84 //注意：Swift除了..还有... 其中..生成前闭后开的区间，而...生成前闭后闭的区间。
85 var third = 0
86 for i in 0...3 {
87     third += i
88 }
89 third