About Swift Control flow

Control Flow If

• There is no concept in the C language in Swift 非零即真
• must indicate the specific condition of judgment in the logical Judgment truefalse
• The IF statement condition () can be omitted
• But {} you can't omit it.

let num = 200if num < 10 {    print("比 10 小")} else if num > 100 { print("比 100 大")} else { print("10 ~ 100 之间的数字")}

Trinocular operation

• Operations in Swift 三目 maintain the same style as OC

var a = 10var b = 20let c = a > b ? a : bprint(c)

Use trinocular appropriately to make the code more concise

Optional type judgment

• Because the content of the optional type may be nil , and once is nil not allowed to participate in the calculation
• Therefore, in practical development, it is often necessary to determine whether the content of an optional type isnil

Single selectable type judgment

Let URL =nsurl (string:  "http://www.baidu.com") //: Method 1: Forcibly unpacking-defect, if the URL is empty, the runtime crashes let request = nsurlrequest (url:url!) //: Method 2: First judgment-the code still needs to use '! ' Force unpack if url! = nil {let request = nsurlrequest (url:url!)} //: Method 3: Use ' If let ', which means that once you enter the IF branch, you are not in the optional type if let u = URL where u.host = " www.baidu.com "{let request = nsurlrequest (url:u)}   

Optional type condition judgment

//: 1> 初学 swift 一不小心就会让 if 的嵌套层次很深，让代码变得很丑陋if let u = url {    if u.host == "www.baidu.com" { let request = NSURLRequest(URL: u) }}//: 2> 使用 where 关键字，if let u = url where u.host == "www.baidu.com" { let request = NSURLRequest(URL: u)}

• Summary
  • if letCan not be judged with the use && , || equal conditions
  • If you want to increase the condition, you can use the where clause
  • NOTE: where clauses do not have smart hints

Multiple optional types to judge

//: 3> can use ', ' to also determine if multiple optional types are empty let oname: String? = "Zhang San" letsoNo: Int? = + if let na me = oname { if let no = oNo { print ("Name:" + name + "study number:" + String (NO))}}if let Name = Oname, let no = oNo { print ("Name:" + name + "study number:" + String (NO))} /c17> 

The variable needs to be modified after judging

let oName: String? = "张三"let oNum: Int? = 18if var name = oName, num = oNum { name = "李四" num = 1 print(name, num)}

Guard

• guardis with the if let opposite syntax, the Swift 2.0 launches the

 let oname: string? = " Zhang San "let onum: int? =  18guard let name = Oname else { Print ( "name is empty") return}guard let num = onum else {print ( "num is empty") Span class= "Hljs-keyword" >return}//code execution to this point, name & Num are all valued print (name) print (num)       

• When the program is written, the code after the conditional detection is relatively complex
• Benefits of using Guard
  • Be able to judge every single value
  • In the True Code Logic section, a layer of nesting is omitted.

Switch

• switchNo longer limited to integers
• switchCan be 任意数据类型 judged against
• No longer neededbreak
• caseThere must be statements that can be executed after each one.
• To ensure that all possible situations are handled, otherwise the compiler will directly error, the conditions can be placed in the default branch
• casethe variables defined in each are only valid in the current case , while OC requires the use of a{}

 let score =  "excellent" switch score {case " excellent ": let name =  "student" print (name +  "80~100 min") case  "good": print ( "70~80 min") case print ( "60~70 min") case  "difference": print (" failed ") default: break}     

• Switch can also be used to assign values and use where clauses

Let point =Cgpoint (x:Ten, Y:10)Switch Point {CaseLet Pwhere p.x = =0 && P.y = =0:print ( "center point") case let p where p.x =  0: print ( "y-axis") case let p where p.y =  0: print ( "x axis") case let p where abs (p.x) = = abs (p.y): print ( "diagonal") default: print ( "other")}    

• If you only want to make conditional judgments, the assignment part can be omitted

switch score {case _ where score > 80: print("优")case _ where score > 60: print("及格")default: print("其他")}

About Swift Control flow