swift 的循环

 在swift中没有隐试转换，swift会根据你写的值推测类型，数组的话它根据第一个来判断

  --for each 循环

for后面写你定义的变量

in后面写你要遍历的对象

   

 let individualScores = [75, 43, 103, 87, 12] 
var teamScore = 0 3. 
for score in individualScores { 
if score > 50 { 
teamScore += 3 
} else { 
teamScore += 1 8. } 
}

-----------if循环

变量可以在if里面定义 let name

在String中写入一个值：写一个值在括号里，和写一个反下斜线（）在括号前

optionalNanme 可选的值，可能会丢失

var optionalName: String? = "John Appleseed" 
var greeting = "Hello!" 
if let name = optionalName { 
greeting = "Hello, (name)" 
}

-------  switch循环

这里可看到switch中的case可一有多个条件，并不是简单的对等

let vegetable = "red pepper" 
switch vegetable { 
case "celery": 
let vegetableComment = "Add some raisins and make ants on a log." 
case "cucumber", "watercress": 
let vegetableComment = "That would make a good tea sandwich." 
case let x where x.hasSuffix("pepper"): 
let vegetableComment = "Is it a spicy (x)?" 
default: 
let vegetableComment = "Everything tastes good in soup." 
}

------for循环

啥时候用for循环，在一中范围内的循环，开始，有结束

var secondForLoop = 0

   for var i = 0; i < 3; ++i {

   secondForLoop += 1 

    }

 secondForLoop

 

var firstForLoop = 0

for i in 0..3 {

 firstForLoop += i

}

 firstForLoop

--------内嵌套循环

找三个数组中的最大值

(kind, numbers) 代表了 kind代表""里的东西
number代表了那个数组

用(kind, numbers)来循环数组
用number来循环数组里的数

let interestingNumbers = [

 "Prime": [2, 3, 5, 7, 11, 13],

 "Fibonacci": [1, 1, 2, 3, 5, 8],

 "Square": [1, 4, 9, 16, 25],

 ]

 var largest = 0

 for (kind, numbers) in interestingNumbers {

 for number in numbers {

if number > largest {

 largest = number

 }

}

 }

 largest

 --------------------------while循环--do--while--

下面两个循环运行结果是一样的，但do-while是无论如何都会执行一次，而while是在满足条件才会执行；

var n = 2

 while n < 100 {

 n = n * 2

}

n

 var m = 2

do {

m = m * 2

} while m < 100

 m