The Swift Programming Language-官方教程精译Swift（6）控制流--Control Flow

1 let numberOfLegs = ["spider": 8, "ant": 6, "cat": 4] 
2 for (animalName, legCount) in numberOfLegs { 
3     println("\(animalName)s have \(legCount) legs") 
4 } 
5 // spiders have 8 legs 
6 // ants have 6 legs 
7 // cats have 4 legs 

1 initialization 
2 while condition { 
3     statements 
4     increment 
5 } 

1 board[03] = +08; board[06] = +11; board[09] = +09; board[10] = +02 
2 board[14] = -10; board[19] = -11; board[22] = -02; board[24] = -08 

1 let finalSquare = 25 
2 var board = Int[](count: finalSquare + 1, repeatedValue: 0) 
3 board[03] = +08; board[06] = +11; board[09] = +09; board[10] = +02 
4 board[14] = -10; board[19] = -11; board[22] = -02; board[24] = -08 
5 var square = 0 
6 var diceRoll = 0 

1 temperatureInFahrenheit = 40 
2 if temperatureInFahrenheit <= 32 { 
3     println("It‘s very cold. Consider wearing a scarf.") 
4 } else { 
5     println("It‘s not that cold. Wear a t-shirt.") 
6 } 
7 // prints "It‘s not that cold. Wear a t-shirt." 

1 temperatureInFahrenheit = 90 
2 if temperatureInFahrenheit <= 32 { 
3     println("It‘s very cold. Consider wearing a scarf.") 
4 } else if temperatureInFahrenheit >= 86 { 
5     println("It‘s really warm. Don‘t forget to wear sunscreen.") 
6 } else { 
7     println("It‘s not that cold. Wear a t-shirt.") 
8 } 
9 // prints "It‘s really warm. Don‘t forget to wear sunscreen." 

1 temperatureInFahrenheit = 72 
2 if temperatureInFahrenheit <= 32 { 
3     println("It‘s very cold. Consider wearing a scarf.") 
4 } else if temperatureInFahrenheit >= 86 { 
5     println("It‘s really warm. Don‘t forget to wear sunscreen.") 
6 } 

 1 let someCharacter: Character = "e" 
 2 switch someCharacter { 
 3 case "a", "e", "i", "o", "u": 
 4     println("\(someCharacter) is a vowel") 
 5 case "b", "c", "d", "f", "g", "h", "j", "k", "l", "m", 
 6 "n", "p", "q", "r", "s", "t", "v", "w", "x", "y", "z": 
 7     println("\(someCharacter) is a consonant") 
 8 default: 
 9     println("\(someCharacter) is not a vowel or a consonant") 
10 } 
11 // prints "e is a vowel" 

1 let anotherCharacter: Character = "a" 
2 switch anotherCharacter { 
3 case "a": 
4 case "A": 
5     println("The letter A") 
6 default: 
7     println("Not the letter A") 
8 } 
9 // this will report a compile-time error 

 1 let count = 3_000_000_000_000 
 2 let countedThings = "stars in the Milky Way" 
 3 var naturalCount: String 
 4 switch count { 
 5 case 0: 
 6     naturalCount = "no" 
 7 case 1...3: 
 8     naturalCount = "a few" 
 9 case 4...9: 
10     naturalCount = "several" 
11 case 10...99: 
12     naturalCount = "tens of" 
13 case 100...999: 
14     naturalCount = "hundreds of" 
15 case 1000...999_999: 
16     naturalCount = "thousands of" 
17 default: 
18     naturalCount = "millions and millions of" 
19 } 
20 println("There are \(naturalCount) \(countedThings).") 
21 // prints "There are millions and millions of stars in the Milky Way." 

 1 let somePoint = (1, 1) 
 2 switch somePoint { 
 3 case (0, 0): 
 4     println("(0, 0) is at the origin") 
 5 case (_, 0): 
 6     println("(\(somePoint.0), 0) is on the x-axis") 
 7 case (0, _): 
 8     println("(0, \(somePoint.1)) is on the y-axis") 
 9 case (-2...2, -2...2): 
10     println("(\(somePoint.0), \(somePoint.1)) is inside the box") 
11 default: 
12     println("(\(somePoint.0), \(somePoint.1)) is outside of the box") 
13 } 
14 // prints "(1, 1) is inside the box" 

 1 let anotherPoint = (2, 0) 
 2 switch anotherPoint { 
 3 case (let x, 0): 
 4     println("on the x-axis with an x value of \(x)") 
 5 case (0, let y): 
 6     println("on the y-axis with a y value of \(y)") 
 7 case let (x, y): 
 8     println("somewhere else at (\(x), \(y))") 
 9 } 
10 // prints "on the x-axis with an x value of 2" 

 1 let yetAnotherPoint = (1, -1) 
 2 switch yetAnotherPoint { 
 3 case let (x, y) where x == y: 
 4     println("(\(x), \(y)) is on the line x == y") 
 5 case let (x, y) where x == -y: 
 6     println("(\(x), \(y)) is on the line x == -y") 
 7 case let (x, y): 
 8     println("(\(x), \(y)) is just some arbitrary point") 
 9 } 
10 // prints "(1, -1) is on the line x == -y" 

 1 let puzzleInput = "great minds think alike" 
 2 var puzzleOutput = "" 
 3 for character in puzzleInput { 
 4     switch character { 
 5     case "a", "e", "i", "o", "u", " ": 
 6         continue 
 7     default: 
 8     puzzleOutput += character 
 9     } 
10 } 
11 println(puzzleOutput) 
12 // prints "grtmndsthnklk" 

 1 let numberSymbol: Character = "三"  // Simplified Chinese for the number 3 
 2 possibleIntegerValue: Int? 
 3 switch numberSymbol { 
 4 case "1", "?", "一", "?": 
 5     possibleIntegerValue = 1 
 6 case "2", "?", "二", "?": 
 7     possibleIntegerValue = 2 
 8 case "3", "?", "三", "?": 
 9     possibleIntegerValue = 3 
10 case "4", "?", "四", "?": 
11     possibleIntegerValue = 4 
12 default: 
13     break 
14 } 
15 if let integerValue = possibleIntegerValue { 
16     println("The integer value of \(numberSymbol) is \(integerValue).") 
17 } else { 
18     println("An integer value could not be found for \(numberSymbol).") 
19 } 
20 // prints "The integer value of 三 is 3." 

 1 let integerToDescribe = 5 
 2 var description = "The number \(integerToDescribe) is" 
 3 switch integerToDescribe { 
 4 case 2, 3, 5, 7, 11, 13, 17, 19: 
 5     description += " a prime number, and also" 
 6     fallthrough 
 7 default: 
 8     description += " an integer." 
 9 } 
10 println(description) 
11 // prints "The number 5 is a prime number, and also an integer." 

1 label name: while condition { 
2     statements 
3 } 

1 let finalSquare = 25 
2 var board = Int[](count: finalSquare + 1, repeatedValue: 0) 
3 board[03] = +08; board[06] = +11; board[09] = +09; board[10] = +02 
4 board[14] = -10; board[19] = -11; board[22] = -02; board[24] = -08 
5 var square = 0 
6 var diceRoll = 0 

 1 gameLoop: while square != finalSquare { 
 2     if ++diceRoll == 7 { diceRoll = 1 } 
 3     switch square + diceRoll { 
 4     case finalSquare: 
 5         // diceRoll will move us to the final square, so the game is over 
 6         break gameLoop 
 7     case let newSquare where newSquare > finalSquare: 
 8         // diceRoll will move us beyond the final square, so roll again 
 9         continue gameLoop 
10     default: 
11         // this is a valid move, so find out its effect 
12         square += diceRoll 
13         square += board[square] 
14     } 
15 } 
16 println("Game over!")