Swift之流程控制

本文首发于个人我的博客

if-else

• if后面的条件能够省略小括号
• 条件后面的大括号不能够省略

下面的代码是能够的

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

复制代码

• if后面的条件只能是bool类型

例以下面是不能够的

if score {
    print("aa")
}
复制代码

while

先看以下代码

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


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

复制代码

• repeat-while 至关于C语言中的 do-while
• 上面代码中没有用num--，是由于从Swift3开始，去掉了自增(++)、自减(--)运算符

for

闭区间运算符: 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])
}
//结果为
//zhangsan
//lisi
//wanger
//mazi

复制代码

• 咱们也能够用range来表示区间，例如

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

复制代码

• 咱们也能够用变量来表示区间，例如

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

复制代码

• 咱们也能够用变量和数值共同使用来表示区间，例如

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

复制代码

半开区间运算符：a..<b 表示 a <= 取值 < b

例如

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

复制代码

3. 区间运算符用在数组上 例如

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

复制代码

• 单侧区间

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

复制代码

或者

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

复制代码

区间类型

以下三种

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

字符、煮饭吃也能够使用区间运算符，但默认不能使用在for-in中 例如

这样写是能够的
let strRange = "a"..."f"
strRange.contains("d") // true
strRange.contains("l") // false

可是下面是会报错的
for i in strRange {
    print(i)
}
复制代码

• \0 到 "~" 包括了全部的要用到的ASCII字符 例如咱们要判断一个字符是不是ASCII字符

let characterRange: ClosedRange<Character> = "\0"..."~"
//想判断s是不是ASCII字符能够
characterRange.contains("s") //返回true
复制代码

带间隔的区间值

用到了 stride 看代码

let all = 100
let interval = 20
// res的取值为从 10 开始 每次间隔 20，直到100结束，
for res in stride(from: 10, to: all, by: interval) {
    print(res)
}// 结果为
//10
//30
//50
//70
//90

复制代码

switch

• case、default 后面不能写大括号{}
• 默承认以不写break，并不会贯穿到后面的条件

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")
}
// 输出为 res = 1
复制代码

关键字 fallthrough

若是咱们想让其贯穿下去，就是用 fallthrough 这个关键字 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")
}
// 输出为
// res = 1
// res = 2
复制代码

switch中支持 字符串，字符类型

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

字符类型
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

复制代码

区间、元组匹配

• 能够用下划线_ 忽略某个值
• 能够对区间，和元组进行匹配

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
复制代码

和

let point = (1,0)
switch point {
case (0, 0):
    print("原点")
case (_, 0):
    print("x轴")
case (0, _):
    print("y轴")
case (-2...2, -2...2):
    print("区间")

default:
     print("other")
}
//x轴
复制代码

值绑定

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

复制代码

where

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

复制代码

标签语句

标签语句用于执行的时候，跳转到标签的位置

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)")
    }
}
输出为 
i == 1, k == 1
i == 1, k == 3
i == 1, k == 4
i == 2, k == 1
i == 2, k == 3
i == 2, k == 4

复制代码

若是加了标签

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)")
    }
   
}
输出为 
i == 1, k == 1
i == 2, k == 1

复制代码

参考资料:

从入门到精通Swift编程

Swift官方源码