Swift---5.流程控制

• 循环语句
• For-in

for num in 1..<5 {
     print(num)
}
//九九乘法表
for time in 1...9 {
     for num in 1...time {
         print("\(num) times \(time) is \(time * num)")
     }
}
//不需要参数,用_代替值
for _ in 1...10 {
     print("这是个循环")
}

• While

var i = 0
while i<10 {
     i += 1
}
repeat {
     i += 1
}while i<20

• 条件语句
• if

var hour = 18
if hour < 6 {
     print("现在是凌晨")
}else if hour < 12 {
     print("现在是早上")
}else if hour < 18 {
     print("现在是中午")
}else {
     print("现在是晚上")
}

• Switch
  • 单一匹配

  var day = "Monday"
  switch day {
  case "Monday":
      print("周一")
  case "Tuesday":
      print("周二")
  case "Wednesday":
      print("周三")
  case "Thursday":
      print("周四")
  case "Friday":
      print("周五")
  case "Saturday":
      print("周六")
  case "Sunday":
      print("周日")
  default:
      print("error")
  }
  

  • 复合匹配

  var day = "Monday"
  switch day {
  case "Monday","Tuesday","Wednesday","Thursday","Friday":
      print("工作日")
  case "Sunday","Sunday":
      print("周末")
  default:
      print("error")
  }
  

  • 区间匹配

  var score = 60
  switch score {
  case 0..<60:
      print("不及格")
  case 60..<75:
      print("及格")
  case 75..<90:
      print("良好")
  case 90...100:
      print("优秀")
  default:
      print("不存在的")
  }
  

  • 元组复合匹配(若做复合匹配,则两个值必须为同类型,且变量名必须相等)

  var code = "404"
  var response = ("404","Not Found")
  switch response {
  case (let code,"Not Found"),("404",let code):
      print("请求失败")
  case (let code,"success "),("200",let code):
      print("请求成功")
  default:
      print("未知错误")
  }
  

• 控制转移语句
• Continue(跳出当前循环,进行下次循环)

var i = 0
for number in 1...10 {
     if number == 5 {
         continue
     }
     //此处i只加了9次,因为当number等于5时,跳出了当前循环
     i += number
}

• Break(跳出整个循环,或者作为Switch语句中的忽略语句,Swift中的Switch,每个分支都必须有相应的操作,当我们想忽略这个分支时,可以用Break)

var i = 0
for number in 1...10 {
     if number == 5 {
         break
     }
   //此处i只加了4次,因为当number等于5时,循环结束了
     i += number
}
var day = "Monday"
switch day {
case "Monday":
     print("周一")
case "Tuesday":
     print("周二")
case "Wednesday":
     print("周三")
case "Thursday":
     print("周四")
case "Friday":
     print("周五")
case "Saturday":
     print("周六")
case "Sunday":
     print("周日")
default:
     break
}

• Fallthrough(贯穿,switch条件中,执行完当前分支语句后,即使不符合下一分支条件,也会继续执行下一分支)

var day = "Monday"
switch day {
case "Monday":
     print("周一要")
     fallthrough
default:
     print("上班")
}

• 带标签的控制语句,在Swift中,我们可以使用一个标签给循环或者条件控制语句命名,方便嵌套时操作对应循环或者条件控制,下述例子中,i只加了4次,因为在第二层循环中,time为5时,跳出了本次循环,进入下一循环,同时time为6时,跳出了firstLoop主循环

var i = 0
firstLoop : for number in 1...10 {
   secondLoop : for time in  1...10
   {
       if time == 5 {
           continue secondLoop
       }
       if time == 6 {
           break firstLoop
       }
       i += time
   }
}

• return(用在方法中,用于调出方法),guard语句,类似于if,提供一个判断,若为假,执行else后的语句,通常使用此方法,在判断某个值时,作为跳出某个方法的依据

var i = 5
func greaterThanZero(number:Int) {
   guard number > 0 else {
       return
   }
   print("数字\(number)大于0")
}
greaterThanZero(number: i)