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if-else

• if后面的條件可以省略小括號(hào)
• 條件后面的大括號(hào)不可以省略

下面的代碼是可以的

let score = 70
if score >= 80 {
    print("優(yōu)秀")
}else if score >= 60{
    print("及格")
}else{
    print("不及格")
}

• if后面的條件只能是bool類型

例如下面是不可以的

if score {
    print("aa")
}

while

先看如下代碼

var num = 5
while num > 0 {
    print("num is \(num)")
    num -= 1
}// 會(huì)打印五次


var num2 = 5
repeat {
    print("num is \(num)")
}while num > 0// 會(huì)打印五次

• repeat-while 相當(dāng)于C語(yǔ)言中的 do-while
• 上面代碼中沒(méi)有用num--，是因?yàn)閺腟wift3開(kāi)始，去掉了自增(++)、自減(--)運(yùn)算符

for

閉區(qū)間運(yùn)算符: a...b，代表著: a <= 取值 <= b

例如

let persons = ["zhangsan","lisi","wanger","mazi"]
for i in 0...3 {
    print(persons[i])
}
//結(jié)果為
//zhangsan
//lisi
//wanger
//mazi

• 我們也可以用range來(lái)表示區(qū)間，例如

let persons = ["zhangsan","lisi","wanger","mazi"]
let range = 0...3
for i in range {
    print(persons[i])
}
//結(jié)果為
//zhangsan
//lisi
//wanger
//mazi

• 我們也可以用變量來(lái)表示區(qū)間，例如

let persons = ["zhangsan","lisi","wanger","mazi"]
let before = 0
var end = 3
for i in before...end {
    print(persons[i])
}
//結(jié)果為
//zhangsan
//lisi
//wanger
//mazi

• 我們也可以用變量和數(shù)值共同使用來(lái)表示區(qū)間，例如

let persons = ["zhangsan","lisi","wanger","mazi"]
for i in before...3 {
    print(persons[i])
}
//結(jié)果為
//zhangsan
//lisi
//wanger
//mazi

半開(kāi)區(qū)間運(yùn)算符：a..<b 表示 a <= 取值 < b

例如

let persons = ["zhangsan","lisi","wanger","mazi"]
for i in 1..<3 {
    print(persons[i])
}
//結(jié)果為
//lisi
//wanger

3. 區(qū)間運(yùn)算符用在數(shù)組上
   例如

let nums = [1,2,3,4]
for num in nums[0...3] {
    print(num)
}
//結(jié)果為
//1
//2
//3
//4

• 單側(cè)區(qū)間

let nums = [1,2,3,4]
for num in nums[0...] {
    print(num)
}
//結(jié)果為
//1
//2
//3
//4

或者

let nums = [1,2,3,4]
for num in nums[..<4] {
    print(num)
}
//結(jié)果為
//1
//2
//3
//4

區(qū)間類型

如下三種

• let range1: ClosedRange<Int> = 1...3
• let range2: Range<Int> = 1..<3
• let range3: PartialRangeThrough<Int> = ...5

字符、煮飯吃也可以使用區(qū)間運(yùn)算符，但默認(rèn)不能使用在for-in中
例如

這樣寫(xiě)是可以的
let strRange = "a"..."f"
strRange.contains("d") // true
strRange.contains("l") // false

但是下面是會(huì)報(bào)錯(cuò)的
for i in strRange {
    print(i)
}

• \0 到 "~" 包括了所有的要用到的ASCII字符
  例如我們要判斷一個(gè)字符是否是ASCII字符

let characterRange: ClosedRange<Character> = "\0"..."~"
//想判斷s是否是ASCII字符可以
characterRange.contains("s") //返回true

帶間隔的區(qū)間值

用到了 stride
看代碼

let all = 100
let interval = 20
// res的取值為從 10 開(kāi)始 每次間隔 20，直到100結(jié)束，
for res in stride(from: 10, to: all, by: interval) {
    print(res)
}// 結(jié)果為
//10
//30
//50
//70
//90

switch

• case、default 后面不能寫(xiě)大括號(hào){}
• 默認(rèn)可以不寫(xiě)break，并不會(huì)貫穿到后面的條件

例如

var res = 1
switch res {
case 0:
    print("res = 0")
case 1:
    print("res = 1")
case 2:
    print("res = 2")
default:
     print("other res")
}
// 輸出為 res = 1

關(guān)鍵字 fallthrough

如果我們想讓其貫穿下去，就是用 fallthrough 這個(gè)關(guān)鍵字
例如

var res = 1
switch res {
case 0:
    print("res = 0")
case 1:
    print("res = 1")
case 2:
    print("res = 2")
default:
     print("other res")
}
// 輸出為
// res = 1
// res = 2

switch中支持 字符串，字符類型

例如

字符串
let string = "aaa"
switch string {
case "aaa":
    print("string is aaa")
case "bbb":
    print("string is bbb")
default:
    break
} // string is aaa

字符類型
let character: Character = "a"
switch character {
case "a","A":
     print("string is a or A")
default:
    print("string is not a or A")
} //string is a or A

區(qū)間、元組匹配

• 可以用下劃線_ 忽略某個(gè)值
• 可以對(duì)區(qū)間，和元組進(jìn)行匹配

let count = 8
switch count {
case 0:
    print("0")
case 1..<5:
    print("1到4")
case 5..<10:
    print("5到10")
default:
    break
}
//5到10

和

let point = (1,0)
switch point {
case (0, 0):
    print("原點(diǎn)")
case (_, 0):
    print("x軸")
case (0, _):
    print("y軸")
case (-2...2, -2...2):
    print("區(qū)間")

default:
     print("other")
}
//x軸

值綁定

let point2 = (1,0)
switch point2 {
case (0, 0):
    print("原點(diǎn)")
case (let x, 0):
    print("x軸 x是 \(x)")
case (0, let y):
    print("y軸 y是 \(y)")
case let (x, y):
    print("somewhere else at (\(x),\(y))")
    
default:
    print("other")
}
// x軸 x是 1

where

var numbers = [1,2,3,4,5,]
var sum = 0
for num in numbers where num > 2 {
    sum += num
}
print(sum) //12

標(biāo)簽語(yǔ)句

標(biāo)簽語(yǔ)句用于執(zhí)行的時(shí)候，跳轉(zhuǎn)到標(biāo)簽的位置

例如

outer: for i in 1...4{
    for k in 1...4 {
        if k == 2 {
            continue
        }
        if i == 3 {
            break outer
        }
         print("i == \(i), k == \(k)")
    }
}
輸出為 
i == 1, k == 1
i == 1, k == 3
i == 1, k == 4
i == 2, k == 1
i == 2, k == 3
i == 2, k == 4

如果加了標(biāo)簽

outer: for i in 1...4{
    for k in 1...4 {
        if k == 2 {
            continue outer
        }
        if i == 3 {
            break outer
        }
         print("i == \(i), k == \(k)")
    }
   
}
輸出為 
i == 1, k == 1
i == 2, k == 1

參考資料:

從入門(mén)到精通Swift編程

Swift官方源碼