Swift控制语句

分支语句

 

1. 条件语句 if-else ，基本语法形式如下，其中 “[]” 中 的部分可以省略。

 

if boolean-expression { statement1;  }  [else if boolean-expression    { statement2; }  ] [else  {statement3;  }  ] 

实例：

 

 var number1 = 0;var number2 = 1; var max = 0; if number1 >number2 { max = number1; } else if number1 < number2 { max = number2; } else { max = number1; }println("Themaximum is \(max)")

2 ．多分支语句 switch 它的语法形式如下：

 

switch some value to consider { case value 1: respond to value 1 case value 2,                value 3:respond to value 2 or 3default: otherwise, do something else }

 

每个 case 不需要显式地添加 break ，每个 case 至少有 一条语句。

 

可以比较任何类型。

实例１：

 

let someCharacter: Character ="e" switch someCharacter {case "a", "e", "i","o", "u": println("\(someCharacter) isa vowel")case "b", "c", "d", "f", "g", "h", "j", "k", "l","m", "n", "p", "q", "r", "s", "t", "v", "w", "x", "y", "z":println("\(someCharacter) is a consonant") default: println("\(someCharacter)  is not  a  vowel   or  a consonant") } 

实例２：

 

let count = 3_000 let countedThings = "stars inthe Milky Way"varnaturalCount: Stringswitch count { case 0: naturalCount ="no" case 1...3:naturalCount ="a few" case 4...9:naturalCount ="several" case 10...99: naturalCount ="tens of" case 100...999:naturalCount ="hundreds of" case 1000...999_999:naturalCount ="thousands of" default:naturalCount = "millions and millions of"  } println("There are \(naturalCount) \(countedThings).")

 

 

循环语句

 

while语句

do-while语句

 

for语句

 

for in语句

while 循环

while condition{ statements }vari = 100 varr = 0 vars= 0 vart = 0while i < 1000 {r= i / 100 s=( i - r* 100 ) / 10 t= i - r* 100 - s* 10 if( i == r * r* r + s* s *s + t* t * t){ println ( "i = \(i)" ) }i++}do while 循环 do { statements } while conditionvari = 100 varr = 0 vars= 0 vart = 0do      { r= i / 100 s=( i - r* 100 ) / 10 t= i - r* 100 - s* 10 if( i == r * r* r + s* s *s + t* t * t){ println ("i = \(i)" ) } i++} while i < 1000

for 循环

for initialization; condition; increment {statements}vari= 8 varr = 0 vars= 0forvarj =0; j <=i; j++{ r = j * j s=j * j * jprintln (" 整数为 :\(j) "); println (" 对应的平方和 :\( r)") println ( " 对应的立方和 : \( s ) " ) }

for in 循环

 

用于遍历集合。

1.  遍历范围

 forindex in1...5{ println( " \(index) times 5 is \(index * 5 )" ) }

 

2.  忽略循环变量

 

letbase = 3letpower = 10 varanswer = 1for_ in 1...power { answer *=base } println (" \(base )to the power of \(power )is \(answer ) " )

 

 

3.  遍历数组

 

letnames =[ "Anna" ,"Alex" , "Brian" ,"Jack"] forname innames { println( "Hello, \(name) !" ) }

4.  遍历字典

 letnumberOfLegs =[ "spider" :8 , "ant" :6 , "cat" : 4] for(animalName, legCount) innumberOfLegs { println( " \(animalName) s have \(legCount) legs" ) }

5 .遍历字符串

 

 letnumberOfLegs =[ "spider" :8 , "ant" :6 , "cat" : 4] for(animalName, legCount) innumberOfLegs { println( " \(animalName) s have \(legCount) legs" ) } letnumberOfLegs =[ "spider" :8 , "ant" :6 , "cat" : 4] for(animalName, legCount) innumberOfLegs { println( " \(animalName) s have \(legCount) legs" ) }

1.12.3 跳转语句

 

 •   continue

 •   break

 

•   fallthrough

 

•   return

 

 

 

 

 

1.continue 实例：

 

for var i = 0; i < 100; i++ { if i % 10 == 0 { continue; } println("i = \(i)"); }

2. break 实例：

 

for var i = 0; i < 10;i++ { if i == 3 { break; }println("i = \(i)");} println("Game Over!");

3. fallthrough 实例：

 

let integerToDescribe = 5 var description = "Thenumber \(integerToDescribe) is" switchintegerToDescribe { case 2, 3, 5, 7, 11, 13, 17, 19: description += " a prime number, and also"fallthroughdefault: description += " an integer."} println(description)

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