swift流程控制_03_swift基本使用

  1 //: Playground - noun: a place where people can play
  2 
  3 import UIKit
  4 
  5 
  6 //1.if语句实现条件选择
  7 //（1）单分支
  8 var age = 9
  9 
 10 if age < 10 {
 11     
 12     print("年龄小于10岁")
 13 }
 14 
 15 //(2)双分支 
 16 var oranges = 20
 17 var apples = 30
 18 
 19 if oranges < apples {
 20     
 21     print("苹果多")
 22 } else {
 23     
 24     print("桔子多")
 25 }
 26 
 27 
 28 //(3)多分支
 29 var score = 65
 30 var grade : Character;
 31 
 32 if score >= 90 {
 33     grade = "A"
 34 } else if score >= 80 {
 35     
 36     grade = "B"
 37 } else if score >= 70 {
 38     
 39     grade = "C"
 40 } else if score >= 60 {
 41     
 42     grade = "D"
 43 } else {
 44     grade = "F"
 45 }
 46 
 47 print("grade=\(grade)")
 48 
 49 
 50 //2. switch语句实现条件选择
 51 /*
 52 (1)switch后面的表达式可以整型，浮点型，字符，字符串，数值可以是单个的，也可以是一段范围
 53 (2)case分支不需要加break语句，分支执行完毕以后会自动的跳出switch
 54 (3)必须有default，必须放在所有分支的最后面
 55 (4)每个case必须有至少一条语句,如果想匹配多个条件，可以用一个case将多个条件用逗号隔开
 56 
 57 */
 58 var light = "Green"
 59 
 60 switch light {
 61     
 62 case "Red":
 63     print("停")
 64 case "Yellow","Green":
 65     print("注意小心通过")
 66 default:
 67     print("灯坏了")
 68     
 69 }
 70 
 71 switch score {
 72 case 90...100: //[90,100]
 73     grade = "A"
 74 case 80..<90: //[80,90)
 75     grade = "B"
 76 case 70..<80:
 77     grade = "C"
 78 case 60..<70:
 79     grade = "D"
 80 default:
 81     grade = "F"
 82     
 83 }
 84 
 85 //3.while和do while
 86 var j = 10;
 87 
 88 repeat {
 89     print(j)
 90     j--
 91     
 92 
 93 } while j > 0
 94 
 95 //4. for循环
 96 //当循环体中的操作与循环变量无关时，循环变量可以用_代替
 97 for _ in 0...10 {
 98     print("next")
 99     
100 }
101 
102 //5.控制转移语句
103 //(1)break和continue
104 for  k in 0..<10 {
105     if k == 3 {
106         continue;
107     }
108     
109     print(k)
110 }
111 
112 //(2)fallthrough:用于switch语句中多个条件的混合处理
113 let intergerToDescribe = 5
114 
115 var description = "The number \(intergerToDescribe) is"
116 
117 switch intergerToDescribe {
118 case 2,3,5,7,11,13,17,19:
119     description += " a prime number, and also"
120     fallthrough
121 default:
122     description += " an integer"
123     
124     
125 }
126 
127 print(description)
128 
129 //(3)标签:用于复杂的循环处理，用标签来进行标识流程控制
130 label1:for var x = 0; x < 5; x++ {
131     for var y = 5; y > 0; y-- {
132         
133         if y == x {
134             break label1;
135         }
136         
137         print("(x,y)=(\(x),\(y))")
138         
139     }
140     
141     
142     
143     
144 }