小白如何进入IOS，答案就在这里

  1 //: Playground - noun: a place where people can play
  2 
  3 import UIKit
  4 /*********常量与变量的声明**********/
  5 let a = 5 //定义常量
  6 //a = 6  //常量不能修改
  7 var b = 5
  8 b = 6
  9 //swift中所有的基本类型都是值类型，包括string类型
 10 var c = b
 11 c
 12 b = 88
 13 c
 14 //swift中的类都是大写的
 15 //下面的常量声明是显式指定类型
 16 let i: Float = 5.5 //默认编译器推断的是double
 17 
 18 //常用的类型string,character,bool,float,double,int
 19 
 20 let flag = true
 21 
 22 let str = "hello world"
 23 let ch: Character = "a"
 24 
 25 //元祖(tuple)
 26 //元祖声明的语法就是一个括号，逗号分隔用来存放多个数据
 27 let t = (404,"not found")
 28 let t1 = (1,1,1,2,3,4)
 29 //通过下标来访问元祖
 30 t.0
 31 t.1
 32 
 33 let t2 = (name: "CJ" ,age: 35.5)//不需要给每个成员都取名字
 34 
 35 t2.name
 36 t2.age
 37 let t3: (name: String,age: Float) = ("cj2",46.6)
 38 t3.age
 39 t3.name
 40 
 41 let t4: (String,Float) = ("aaaa",4)
 42 t4.0
 43 t4.1
 44 
 45 let t5:(name: String, Float) = ("bbb",5)
 46 t5.1
 47 
 48 let t6:(String,Float) = (name: "xxxx",age: 55)
 49 t6.0
 50 t6.1
 51 //t6.name //由于在声明的时候没有指定名字，所以不能访问
 52 
 53 //下面的写法（声明的同时就赋值）不行，
 54 //let t8: (name: String = "aaa",age: Float = 222)
 55 
 56 //string类型
 57 
 58 let str1: String
 59 
 60 str1 = "aaaa"
 61 
 62 var  str2   = "bbbb"
 63 str2 = "cccc"
 64 str2 += "dddd"
 65 str2 = "abcdefg"
 66 
 67 str2.characters.count //取字符长度
 68 
 69 str2.startIndex
 70 str2.endIndex
 71 str2[str2.startIndex]
 72 //str2[str2.startIndex + 1]
 73 
 74 str2.index(after: str2.startIndex)
 75 str2[str2.index(after: str2.startIndex)]
 76 str2.index(before: str2.endIndex)
 77 
 78 str2.index(str2.startIndex, offsetBy: 3)
 79 str2[str2.index(str2.startIndex, offsetBy: 3)]
 80 
 81 str2.index(str2.endIndex, offsetBy: -3)
 82 
 83 str2.substring(to: str2.index(str2.startIndex, offsetBy: 3))
 84 
 85 str2.substring(from: str2.index(str2.startIndex, offsetBy: 3))
 86 
 87 str2.uppercased()
 88 str2.lowercased()
 89 str2.capitalized
 90 
 91 str2.hasPrefix("abc") //是否有前缀（prefix）
 92 str2.hasSuffix("abc") //是否有后缀
 93 str2.hasSuffix("g")
 94 str2.hasSuffix("fg")
 95 str2.contains("de") // 是否包含
 96 
 97 i
 98 
 99 let str3 = "abc \(i * 5)"
100 
101 //swift操作符基本与c#，java一样
102 
103 let f = true
104 a
105 
106 if f {
107     print("true")
108 }
109 
110 if (a >= 5 )  {
111     print("da yu dengyu 5")
112 }  else if( a > 3) {
113     
114 } else {
115     
116 }
117 
118 let age = 35
119 switch age {
120 case 25:
121     print("25sui")
122 case 35:
123     print("chenjun")
124 default:
125     print("fei 25")
126 }
127 
128 Int.min
129 Int.max
130 
131 switch age {
132 case 1...60:
133     print("suo you de zhengshu ")
134 default:
135     print("1...60zhiwai")
136 }
137 
138 
139 switch age {
140 case 1,20,35,60:
141     print("suo you de zhengshu ")
142 default:
143     print("1...60zhiwai")
144 }
145 
146 
147 let arr = [1,2,3,4,8,30,5,10]
148 for a in arr {
149     print(a)
150 }
151 
152 
153 for a in 0...3 {
154     print(arr[a])
155 }
156 
157 var max = arr[0]
158 for item in arr {
159     if item % 2 != 0 && item > max {
160         max = item
161     }
162 }
163 max
164 
165 var n = 3
166 while n < 10 {
167     n += 1
168     print(n)
169 }
170 
171 n = 3
172 repeat {
173     print("xxx")
174      n += 1
175 } while  n < 10
176 
177 
178 /********  集合 Array，Dictionary，Set ***/
179 
180 let arr2: Array<Int> = Array<Int>()
181 var arr3 = [1,2,3,3]
182 let arr4: Array<Int> = []
183 
184 
185 arr3[0]
186 
187 arr3.append(5)
188 arr3.append(contentsOf: [6,7,8])
189 arr3
190 arr3 += [10,11]
191 arr3
192 
193 //arr3.insert(contentsOf: <#T##Collection#>, at: <#T##Int#>)
194 
195 //arr3.remove(at: <#T##Int#>)
196 
197 
198 var dic = ["a":"abc","b":"def"]
199 dic["a"]
200 dic["c"] = "ggg"
201 dic.count
202 
203 for k in dic.keys {
204     print(k)
205 }
206 
207 for v in dic.values {
208     print(v)
209 }
210 
211 for (k,v) in dic {
212     print ("key is \(k) value is \(v)")
213 }
214 
215 
216 var s: Set<Int> = [1,2,3,4,4]
217 
218 s.count
219 s.insert(2)
220 
221 s.count
222 
223 var s1: Set<Int> = [2,3,6,7]
224 
225 let r1 = s.intersection(s1)
226 s.union(s1)
227 
228 
229 
230 /*作业
231  1.求出一个字符串中从第三个字符后的所有子字符串
232  2.求出一个数组中所有偶数的和
233  3.求出两个Set的差
234  4.["127":[40,80,90],"130":[60,70,80]]这个字典代表2个班级所有的成绩，求出两个班级的平均分，结果用tuple表示，比如（70，70）
235  
236  额外需要学习的
237  1.找出trim方法
238  2.学习switch没有讲的内容
239  
240  
241  
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