Swift - 控制流/控制结构说明（if，switch，for，while）

一、if 语句

 let count = 7
        
        if count > 1{
            print("yes")
        }else{
            print("no")
        }

 

二、switch 语句 

（1）Swift中不需要在case块中显示地使用break跳出switch。 

let fruit = "apple"
        switch fruit {
        case "aaple":
            print("good")
        case  "banana","orange":
            print("great")
        default:
            print("bad")
            
        }

 （2）case分支还可以进行区间匹配

let age = 3
        switch age {
        case 0...11:
            print("正太")
        case 12...13:
            print("少年")
        default:
            print("中年")
        }

 （3）case分支同样支持单侧区间匹配

let num = 2
        switch num {
        case ..<0:
            print("负数")
        case 0:
            print("零")
        case 0...:
            print("正数")
        default:
            print("未知")
        }

 （4）使用元组匹配（判断属于哪个象限）

let point = (2,2)
        switch point {
        case (0,0):
           print("坐标在原点")
        case (_,0):
           print("坐标在x轴上")
        case (0,_):
           print("坐标在y轴上")
        case (-2...2,-2...2):
            print("坐标在长宽为4的正方形内")
        default:
            print("未知")
        }

 （4）case中还可以使用where关键字来做额外的判断条件

  var height = 2.0
        switch height {
        case 1...3 where height == 1.72:
            print("case 1")
        case 1...3 where height == 2.0:
            print("case 2")
        default:
            print("default")
        }

 

三、for 循环语句 

（1）for-in循环

 for i in 1..<10{
            print("\(i)")
        }
       //遍历数组
        let numbers = [1,2,4,7]
        for num in numbers{
            print("\(num)")
        }

        //遍历字典
        let nameOfAge = ["lily":18,"Candy":24]
        for(aName, iAge)in nameOfAge{
            print("\(aName) is \(iAge)")
        }

        //遍历字符串的字符
        "helloWorld".forEach { (C) in
             print(C)
        }
        (1...10).forEach {
            print($0)
        }

 

四、while 循环语句

var i = 0
        
        while i < 10 {
            i += 1
            print(i)
        }
        
        repeat{
          i += 1
        print(i)
        }while i<100