Swift之流程控制

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if-else

• if後面的條件能夠省略小括號
• 條件後面的大括號不能夠省略

下面的代碼是能夠的

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

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• if後面的條件只能是bool類型

例以下面是不能夠的

if score {
    print("aa")
}
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while

先看以下代碼

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


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

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• repeat-while 至關於C語言中的 do-while
• 上面代碼中沒有用num--，是由於從Swift3開始，去掉了自增(++)、自減(--)運算符

for

閉區間運算符: a...b，表明着: a <= 取值 <= b

例如

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

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• 咱們也能夠用range來表示區間，例如

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

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• 咱們也能夠用變量來表示區間，例如

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

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• 咱們也能夠用變量和數值共同使用來表示區間，例如

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

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半開區間運算符：a..<b 表示 a <= 取值 < b

例如

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

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3. 區間運算符用在數組上 例如

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

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• 單側區間

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

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或者

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

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區間類型

以下三種

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

字符、煮飯吃也能夠使用區間運算符，但默認不能使用在for-in中 例如

這樣寫是能夠的
let strRange = "a"..."f"
strRange.contains("d") // true
strRange.contains("l") // false

可是下面是會報錯的
for i in strRange {
    print(i)
}
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• \0 到 "~" 包括了全部的要用到的ASCII字符 例如咱們要判斷一個字符是不是ASCII字符

let characterRange: ClosedRange<Character> = "\0"..."~"
//想判斷s是不是ASCII字符能夠
characterRange.contains("s") //返回true
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帶間隔的區間值

用到了 stride 看代碼

let all = 100
let interval = 20
// res的取值爲從 10 開始 每次間隔 20，直到100結束，
for res in stride(from: 10, to: all, by: interval) {
    print(res)
}// 結果爲
//10
//30
//50
//70
//90

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switch

• case、default 後面不能寫大括號{}
• 默承認以不寫break，並不會貫穿到後面的條件

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")
}
// 輸出爲 res = 1
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關鍵字 fallthrough

若是咱們想讓其貫穿下去，就是用 fallthrough 這個關鍵字 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")
}
// 輸出爲
// res = 1
// res = 2
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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

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區間、元組匹配

• 能夠用下劃線_ 忽略某個值
• 能夠對區間，和元組進行匹配

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
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和

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

default:
     print("other")
}
//x軸
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值綁定

let point2 = (1,0)
switch point2 {
case (0, 0):
    print("原點")
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

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where

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

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標籤語句

標籤語句用於執行的時候，跳轉到標籤的位置

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)")
    }
}
輸出爲 
i == 1, k == 1
i == 1, k == 3
i == 1, k == 4
i == 2, k == 1
i == 2, k == 3
i == 2, k == 4

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若是加了標籤

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)")
    }
   
}
輸出爲 
i == 1, k == 1
i == 2, k == 1

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參考資料:

從入門到精通Swift編程

Swift官方源碼