一 if關(guān)鍵詞
let age = 4
if age >= 22 {
? ? print("Get married")
} else if age >= 18 {
? ? print("Being a adult")
} else if age >= 7 {
? ? print("Go to school")
} else {
? ? print("Just a child")
}
if后面的條件可以省略小括號?
條件后面的大括號不可以省略
if后面的條件只能是Bool類型
二 while
var num = 5
while num > 0 {
? ? print("num is \(num)")
????num?-=?1?}?//?打印了5次
while-repeat
var num = -1
repeat {
????print("num is?\(num)") }?while?num?>?0?//?打印了1次
repeat-while相當(dāng)于C語言中的do-while
這里不用num--浙值，是因?yàn)閺腟wift3開始，去除了自增(++)放闺、自減(--)運(yùn)算符
for關(guān)鍵字
閉區(qū)間運(yùn)算符:a...b， a <= 取值 <= b
let names = ["Anna", "Alex", "Brian", "Jack"]
for i in 0...3 {
? ? print(names[i])
} // Anna Alex Brian Jack
---------------------------
// i默認(rèn)是let充甚，有需要時可以聲明為var?
for var i in 1...3 {
i += 5
? ? print(i)
} // 6 7 8
------------------------
for _ in 1...3 {
? ? print("for")
} // 打印了3次
-----------------------
let range = 1...3
for i in range {
? ? print(names[i])
} // Alex Brian Jack
------------------------
let a = 1
var b = 2
for i in a...b {
? ? print(names[i])
} // Alex Brian
----------------------
for i in a...3 {
? ? print(names[i])
} // Alex Brian Jack
半開區(qū)間運(yùn)算符:a..<b， a <= 取值 < b
for i in 1..<5 {
? ? print(i)
} // 1 2 3 4
for – 區(qū)間運(yùn)算符用在數(shù)組上
let names = ["Anna", "Alex", "Brian", "Jack"]
for name in names[0...3] {
? ? print(name)
} // Anna Alex Brian Jack
單側(cè)區(qū)間:讓區(qū)間朝一個方向盡可能的遠(yuǎn)
for name in names[2...] {
? ? print(name)
} // Brian Jack
for name in names[...2] {
? ? print(name)
} // Anna Alex Brian
for name in names[..<2] {
? ? print(name)
} // Anna Alex
---------------------------
let range = ...5
range.contains(7) // false
range.contains(4) // true
range.contains(-3) // true
區(qū)間類型
let range1: ClosedRange<Int> = 1...3
let range2: Range<Int> = 1..<3
let range3: PartialRangeThrough<Int> = ...5
字符、字符串也能使用區(qū)間運(yùn)算符堰乔，但默認(rèn)不能用在for-in中
let stringRange1 = "cc"..."ff" // ClosedRange<String>
stringRange1.contains("cb") // false
stringRange1.contains("dz") // true
stringRange1.contains("fg") // false
let stringRange2 = "a"..."f"
stringRange2.contains("d") // true
stringRange2.contains("h") // false
// \0到~囊括了所有可能要用到的ASCII字符
let characterRange: ClosedRange<Character> = "\0"..."~"?
characterRange.contains("G") // true
帶間隔的區(qū)間值
let hours = 11
let hourInterval = 2
// tickMark的取值:從4開始，累加2脐恩，不超過11
for tickMark in stride(from: 4, through: hours, by: hourInterval) {
? ? print(tickMark)
} // 4 6 8 10
switch
case浩考、default后面不能寫大括號{}
var number = 1
switch number {
case 1:
? ? print("number is 1")
break case 2:
? ? print("number is 2")
? ? break
default:
? ? print("number is other")
break
} // number is 1
默認(rèn)可以不寫break，并不會貫穿到后面的條件
var number = 1
switch number {
case 1:
? ? print("number is 1")
case 2:
? ? print("number is 2")
default:
? ? print("number is other")
} // number is 1
fallthrough
使用fallthrough可以實(shí)現(xiàn)貫穿效果
var number = 1
switch number {
case 1:
? ? print("number is 1")
? ? fallthrough
case 2:
? ? print("number is 2")
default:
? ? print("number is other")
}
// number is 1
// number is 2
switch注意點(diǎn)
switch必須要保證能處理所有情況
var number = 1
switch number {
case 1:
? ? print("number is 1")
case 2:
? ? print("number is 2")
}
case被盈、default后面至少要有一條語句,如果不想做任何事析孽，加個break即可
var number = 1
switch number {
case 1:
? ? print("number is 1")
case 2:
? ? print("number is 2")
default:
break
}
如果能保證已處理所有情況，也可以不必使用default
enum Answer { case right, wrong }
let answer = Answer.right
switch answer {
case Answer.right:
? ? print("right")
case Answer.wrong:
? ? print("wrong")
}
// 由于已確定answer是Ansewer類型只怎，因此可以省略Answer?
switch answer {
case .right:
? ? print("right")
case .wrong:
? ? print("wrong")
}
復(fù)合條件
switch也支持Character袜瞬、String類型
let string = "Jack"
switch string {
case "Jack":
? ? fallthrough
case "Rose":
? ? print("Right person")
default:
break
} // Right person
--------------------------
let character: Character = "a"
switch character {
case "a", "A":
? ? print("The letter A")
default:
? ? print("Not the letter A")
} // The letter A
-------------------------
switch string {
case "Jack", "Rose":
? ? print("Right person")
default:
break
} // Right person
區(qū)間匹配、元組匹配
let count = 62
switch count {
case 0:
? ? print("none")
case 1..<5:
? ? print("a few")
case 5..<12:
? ? print("several")
case 12..<100:
? ? print("dozens of")
case 100..<1000:
? ? print("hundreds of")
default:
? ? print("many")
} // dozens of
-----------------------
let point = (1, 1)
switch point {
case (0, 0):
? ? print("the origin")
case (_, 0):
? ? print("on the x-axis")
case (0, _):
? ? print("on the y-axis")
case (-2...2, -2...2):
? ? print("inside the box")
default:
print("outside of the box") } // inside the box
可以使用下劃線 _ 忽略某個值
關(guān)于case匹配問題身堡，屬于模式匹配(Pattern Matching)的范疇邓尤，以后會再次詳細(xì)展開講解
值綁定?必要時let也可以改為var
let point = (2, 0)
switch point {
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))")
} // on the x-axis with an x value of 2
where
let point = (1, -1)
switch point {
case let (x, y) where x == y:
? ? print("on the line x == y")
case let (x, y) where x == -y:
? ? print("on the line x == -y")
case let (x, y):
? ? print("(\(x), \(y)) is just some arbitrary point")
} // on the line x == -y
// 將所有正數(shù)加起來
var numbers = [10, 20, -10, -20, 30, -30]
var sum = 0
for num in numbers where num > 0 { // 使用where來過濾num
sum += num }
print(sum) // 60
標(biāo)簽語句
outer: for i in 1...4 {
? ? for k in 1...4 {
? ? ? ? if k == 3 {
? ? ? ? ? ? continue outer
????????}
????????if i == 3 {
????????????break outer?
????????}
? ? ? ? print("i == \(i), k == \(k)")
? ? }
}
