一.For-in
1. ...
在下面的例子是打印从1到6的数,1...6 1是开头 6是结尾,开头和结尾都包括在其中。
第一个例子：
for index in 1...6{
print("index = \(index)")
}打印:
index = 1 index = 2 index = 3 index = 4 index = 5 index = 6
第二个例子：
这个例子相当于普通的for循环。 for(int i = 1;i < 10;i++)
let base = 3
let power = 10
var answer = 1
for _ in 1...power {
answer *= base
}
print("\(base) to the power of \(power) is \(answer)")打印：
3 to the power of 10 is 59049
2.数组的遍历
let names = ["Anna","Alex","Brian","Jack"]
for name in names {
print("Hello,\(name)!")
}打印：
Hello,Anna! Hello,Alex! Hello,Brian! Hello,Jack!
3.字典的遍历
let numberOfLegs = ["spider": 8,"ant": 6,"cat": 4]
for (animalName,legCount) in numberOfLegs {
print("\(animalName)s have \(legCount) legs")
}打印：
ants have 6 legs cats have 4 legs spiders have 8 legs
4.字符串的遍历
for character in "Dog!".characters {
print(character)
}打印：
D o g !
二、Repeat-While
先执行循环，知道条件为假就结束，和do-while一样。
repeat {
statements
} while condition
三、if
这个没什么好讲的。var temperatureInFahrenheit = 90
if temperatureInFahrenheit <= 32 {
print("It's very cold. Consider wearing a scarf.")
} else if temperatureInFahrenheit >= 86 {
print("It's really warm. Don't forget to wear sunscreen.")
} else {
print("It's not that cold. Wear a t-shirt.")
}打印：
It's really warm. Don't forget to wear sunscreen.
四、Switch
可以多个条件，可以不要break。
switch some value to consider {
case value 1:
respond to value 1
case value 2,value 3:
respond to value 2 or 3
default:
otherwise,do something else
}
例子1：
let someCharacter: Character = "e"
switch someCharacter {
case "a","e","i","o","u":
print("\(someCharacter) is a 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")
}
// prints "e is a vowel"
例子2：
let anotherCharacter: Character = "a"
switch anotherCharacter {
case "a":
print("The letter a")
case "A":
print("The letter A")
default:
print("Not the letter A")
}
// this will report a compile-time error
例子3：
元组的switch - case
let somePoint = (1,1)
switch somePoint {
case (0,0):
print("(0,0) is at the origin")
case (_,0):
print("(\(somePoint.0),0) is on the x-axis")
case (0,_):
print("(0,\(somePoint.1)) is on the y-axis")
case (-2...2,-2...2):
print("(\(somePoint.0),\(somePoint.1)) is inside the Box")
default:
print("(\(somePoint.0),\(somePoint.1)) is outside of the Box")
}
// prints "(1,1) is inside the Box"
例子4：
let anotherPoint = (2,0)
switch anotherPoint {
case (let x,0):
print("on the x-axis with an x value of \(x)")
case (0,let y):
print("on the y-axis with a y value of \(y)")
case let (x,y):
print("somewhere else at (\(x),\(y))")
}
// prints "on the x-axis with an x value of 2"
例子5：where
let yetAnotherPoint = (1,-1)
switch yetAnotherPoint {
case let (x,y) where x == y:
print("(\(x),\(y)) is on the line x == y")
case let (x,y) where x == -y:
print("(\(x),\(y)) is on the line x == -y")
case let (x,y):
print("(\(x),\(y)) is just some arbitrary point")
}
// prints "(1,-1) is on the line x == -y"
例子6：Continue
let puzzleInput = "great minds think alike"
var puzzleOutput = ""
for character in puzzleInput.characters {
switch character {
case "a","u"," ":
continue
default:
puzzleOutput.append(character)
}
}
print(puzzleOutput)
// prints "grtmndsthnklk"打印的时case之外的字符串
例子7：break
let numberSymbol: Character = "三" // Simplified Chinese for the number 3
var possibleIntegerValue: Int?
switch numberSymbol {
case "1","١","一","๑":
possibleIntegerValue = 1
case "2","٢","二","๒":
possibleIntegerValue = 2
case "3","٣","三","๓":
possibleIntegerValue = 3
case "4","٤","四","๔":
possibleIntegerValue = 4
default:
break
}
if let integerValue = possibleIntegerValue {
print("The integer value of \(numberSymbol) is \(integerValue).")
} else {
print("An integer value could not be found for \(numberSymbol).")
}
// prints "The integer value of 三 is 3."
例子8：fallthrough
let integerToDescribe = 5
var description = "The number \(integerToDescribe) is"
switch integerToDescribe {
case 2,3,5,7,11,13,17,19:
description += " a prime number,and also"
fallthrough
default:
description += " an integer."
}
print(description)
// prints "The number 5 is a prime number,and also an integer."
例子9：#available
检查API的有效性
if #available(platform name version,...,*) {
statements to execute if the APIs are available
} else {
fallback statements to execute if the APIs are unavailable
}
if #available(iOS 9,OSX 10.10,*) {
// Use iOS 9 APIs on iOS,and use OS X v10.10 APIs on OS X
} else {
// Fall back to earlier iOS and OS X APIs
}
