For-In Loops
很简单，直接看代码：
/* 遍历数组 */
let names = ["Anna", "Alex", "Brian", "Jack"]
for name in names {
print("Hello, \(name)!")
}
// Hello, Anna!
// Hello, Alex!
// Hello, Brian!
// Hello, Jack!
/* 遍历字典 */
let numberOfLegs = ["spider": 8, "ant": 6, "cat": 4]
for (animalName, legCount) in numberOfLegs {
print("\(animalName)s have \(legCount) legs")
}
// cats have 4 legs
// ants have 6 legs
// spiders have 8 legs
/* 遍历范围 */
for index in 1...5 {
print("\(index) times 5 is \(index * 5)")
}
// 1 times 5 is 5
// 2 times 5 is 10
// 3 times 5 is 15
// 4 times 5 is 20
// 5 times 5 is 25
/* 不需要数组信息，只需遍历次数 */
let base = 3
let power = 10
var answer = 1
for _ in 1...power {
answer *= base
}
print("\(base) to the power of \(power) is \(answer)")
// Prints "3 to the power of 10 is 59049
/* 遍历左闭右开区间 */
let minutes = 60
for tickMark in 0..<minutes {
// render the tick mark each minute (60 times)
}
/* 遍历跳步区间，使用stride(from:to:by:)，注意是左闭右开 */
let minuteInterval = 5
for tickMark in stride(from: 0, to: minutes, by: minuteInterval) {
// render the tick mark every 5 minutes (0, 5, 10, 15 ... 45, 50, 55)
}
/* 遍历跳步区间，使用stride(from:through:by:)，注意是左闭右闭 */
let hours = 12
let hourInterval = 3
for tickMark in stride(from: 3, through: hours, by: hourInterval) {
// render the tick mark every 3 hours (3, 6, 9, 12)
}
While Loops
先判断再循环
while condition {
statements
}
先循环再判断
repeat {
statements
} while condition
Conditional Statements
if适合情况少
switch适合情况复杂
if
if condition1 {
statement1
} else if condition2 {
statement2
} else {
statement of other condition
}
Switch
switch some value to consider {
case value1:
respond to value 1
case value2, value3:
respind to value 2 or 3
default:
otherwise, do something else
}
No Implicit Fallthrough
Swift的switch不需要break去结束符合的情况，但是你仍然可以使用break。
并且case里面的结构体不允许是空的。
Interval Matching
switch也可以判断区间
let approximateCount = 62
let countedThings = "moons orbiting Saturn"
let naturalCount: String
switch approximateCount {
case 0:
naturalCount = "no"
case 1..<5:
naturalCount = "a few"
case 5..<12:
naturalCount = "several"
case 12..<100:
naturalCount = "dozens of"
case 100..<1000:
naturalCount = "hundreds of"
default:
naturalCount = "many"
}
print("There are \(naturalCount) \(countedThings).")
// Prints "There are dozens of moons orbiting Saturn.
Tuples
switch也可以判断tuples，并且可以使用_匹配任何可能。
let somePoint = (1, 1)
switch somePoint {
case (0, 0):
print("\(somePoint) is at the origin")
case (_, 0):
print("\(somePoint) is on the x-axis")
case (0, _):
print("\(somePoint) is on the y-axis")
case (-2...2, -2...2):
print("\(somePoint) is inside the box")
default:
print("\(somePoint) is outside of the box")
}
// Prints "(1, 1) is inside the box
Value Bindings
在switch结构体里面，将判断值绑定到一个临时量，以便使用。
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
Where
在绑定值的同时，还可以用where制定条件。
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
Compound Cases
let stillAnotherPoint = (9, 0)
switch stillAnotherPoint {
case (let distance, 0), (0, let distance):
print("On an axis, \(distance) from the origin")
default:
print("Not on an axis")
}
// Prints "On an axis, 9 from the origin
Control Transfer Statements
Swift的五个控制转移语句：
continuebreakfallthroughreturnthrow
Continue
结束本轮循环，直接开始下一轮循环。
Break
结束循环体，结束switch语句体。
Fallthrough
在switch中，可以使用fallthrough去继续执行下一个case，而不是匹配到一个case之后直接退出switch
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.
Labeled Statements
在嵌套while和switch等控制流的时候，因为单纯的break和continue只能对最近的控制流起作用。
Swift可以给控制流贴上标签，因此break和continue就可以指定作用在哪个控制流了。
gameLoop: while square != finalSquare {
diceRoll += 1
if diceRoll == 7 { diceRoll = 1 }
switch square + diceRoll {
case finalSquare:
// diceRoll will move us to the final square, so the game is over
break gameLoop // 在switch里面结束while的所有
case let newSquare where newSquare > finalSquare:
// diceRoll will move us beyond the final square, so roll again
continue gameLoop // 在switch里面结束while的一轮
default:
// this is a valid move, so find out its effect
square += diceRoll
square += board[square]
}
}
print("Game over!")
Early Exit
如果condition为false就执行else
guard conditon else {
statement
}
例子：
func greet(person: [String: String]) {
guard let name = person["name"] else {
return
}
print("Hello \(name)!")
guard let location = person["location"] else {
print("I hope the weather is nice near you.")
return
}
print("I hope the weather is nice in \(location).")
}
greet(person: ["name": "John"])
// Prints "Hello John!"
// Prints "I hope the weather is nice near you."
greet(person: ["name": "Jane", "location": "Cupertino"])
// Prints "Hello Jane!"
// Prints "I hope the weather is nice in Cupertino.
Checking API Availability
if #available(iOS 10, macOS 10.12, *) {
// Use iOS 10 APIs on iOS, and use macOS 10.12 APIs on macOS
} else {
// Fall back to earlier iOS and macOS APIs
}
