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 = 0for 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 = 2do {m = m * 2} while m < 100 m