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swift语言基础（二）流程控制

2016-01-07 22:48 399 查看

关于流程控制，其实swift语言中的流程控制与大多数语法规则有着差不多的相似之处。以下就是我通过对官网的学习：

代码开源

  for语句

let individualScores = [75,43,103,87,12]

var teamScore = 0

for score in individualScores{

if score > 50{

teamScore += 3

}else{

teamScore += 1

}

}

print(teamScore)



对于空值，可以在类型声明后添加“？”，显式标明该类型可以为空

var optionalString:String? = "hello"

optionalString = nil

let defaultColorName = "red"

let colorNameToUse = optionalString ?? defaultColorName//如果前者为空返回后者，如果前者不为空就返回前者。

print(colorNameToUse)



let optionalName:String? = "John Appleseed"

var gretting = "Hello!"

if let name = optionalName {

gretting = "Hello,\(name)"//\(常量或者变量名)这样用于插入某个字符串中

}

print(gretting)



for-in对于数据范围／序列／集合等中的每一个元素，都执行一次。

for index in 1...5{//1...5表示1到5这个范围

print("\(index) times is \(index * 5)")

}

for－condition-increment一直执行，直到特定的条件满足，每一次执行，都增加一个计数。

如果不需要序列中的每一个值用“_”来忽略它，只执行循环本身

let base = 3

let power = 10

var answer = 1

for _ in 1...power {

answer *= base

print(answer)

}

print("\(base) to the power of \(power) is \(answer)")



遍历字典

let interestingNumber = ["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 interestingNumber {

print("\(kind) is \(numbers)")

}

for (_ , numbers) in interestingNumber {

for number in numbers {

if number > largest {

largest = number

}

}

}

print(largest)



OC中的循环表达方法

for var index = 0; index < 3; ++index {

print("index is \(index)")//如果想要在循环后继续使用index的话，要在循环之前定义好。

}



//while循环

let finalSquare = 25

var board = [Int](count:finalSquare + 1, repeatedValue:0)

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

var square = 0

var diceRoll = 0

while square < finalSquare {

if ++diceRoll == 7 { diceRoll = 1}

square += diceRoll

if square < board.count {

square += board[square]

}

print(square)

}

print(board)



repeat {//这里和C不一样，用的repeat

square += board[square]

if ++diceRoll == 7 {diceRoll = 1}

square += diceRoll

print(square)

}while square < finalSquare

print("Game over")

与c语言一样只是条件不用加括号





条件语句

var temperatureInFahrenherit = 30

if temperatureInFahrenherit <= 32 {

print("It's very cold .Consider wearing a scarf")

}



temperatureInFahrenherit = 40

if temperatureInFahrenherit <= 32 {

print("It's very cold. Consider wearing a scarf")

}else {

print("It's not that cold .Wear a t-shirt")

}



多分支判断与C语言一样只是条件没有括号。



switch语句

let someCharacter:Character = "e"

switch someCharacter {

case "a","e","i","o","u":

print("\(someCharacter) is vowel")

case "b","c","d","f","g","h","j","k","l","m","n","p","q","r","s","t","v","w","x","y","z":

print("\(someCharacter) is a consonant")

default:

print("\(someCharacter) is not a vowel or a consonant")

}

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标签： swift 语言流程控制

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