Swift语法(一)

Swift语法

1.前言

之前学过siwft语法，但是没有整理，这边简易总结简单语法。

2.HelloWorld

print("Hello World")

3.常量与变量

• 常量

swift支持让let作为常量，并且支持类型推断。

let PI = 3.1415
let PI2: Double = 3.1415

print(PI)

• 变量

swift支持使用var进行申明变量，并且变量支持Unicode编码

var width = 150
var width2: Int = 150
var π = 3.1415
var 🤠 = "laugh"
var 中文 = "中文"

4.类型与特征

数据类型

• Int 整型
• UInt 无符号整型
• Float、Double 浮点
• Bool 布尔
• String 字符串
• Character 字符
• Optional 可选类型
• Tuple 元祖

数据特征

• 别名 typealias Feet = Int
• 类型推断 let age = 40

let a: Int = 1
let b: UInt = 2
let c: Float = 1.1
let d: Double = 0.11
let e: Bool = true
let f: String = "Hello"
let g: Character = "A" // 注意Character需要使用双引号
let (on, tw): (Int, Int) = (1, 2)
print(on, tw)
let i: (String, Int) = ("hi", 2)
let hi = i.0
let two = i.1
print(hi, two)
// 可选类型
let address: String?
let age: Int?

5.基础操作符

几乎和c一致

var a = 6
var b = -a
var c = a + b
var d = a / b
var e = 5 % 2
var f = a >= b
var g = a <= b
var h = a == b

6.集合类型

数组

var arr = [1, 2, 3]
var arr2 = [Int](repeating: 3, count: 10)
var arr3 = Array(1...20)
var places = ["北京", "上海"]

• 计数

//计数
print(arr.count)

• 添加元素

//添加元素
arr.append(4)
arr += [5, 6, 7]

• 插入

//插入
places.insert("Paries", at: 1)

• 删除

//删除元素
places.remove(at: 1)
print(places)

• 查询

// 查询
print(places[0...1])
print(places[0])

集合

• 增加

var cardno: Set = [1, 2, 3]
cardno.insert(1)
cardno.insert(4)
print(cardno)

• 删除

cardno.remove(3)
print(cardno)

• 检查

cardno.contains(1)

• 转换数组

let arr: Array<Int> =  cardno.sorted()
print(type(of: arr))

• 交叉并补

var arr: Set<Int> = [1, 2, 3]
var arr2: Set<Int> = [2, 3, 4]
var arr3: Set<Int> = arr.intersection(arr2)
var arr4: Set<Int> = arr.subtracting(arr2)
var arr5: Set<Int> = arr.union(arr2)
var arr6: Set<Int> = arr.symmetricDifference(arr2)

字典

• 字典的取值

var dic = ["apple": 1.1, "banana": 1]
print(dic["apple"]!) // 取值不存在返回nil

• 添加更新

dic["pear"] = 1

• count

print(dic.count)

7.循环控制

• for in循环

var arr = [1, 2, 3, 4, 5]
for ele in arr {
    print(ele)
}
for ele in 1...100 {
    print(ele)
}
for _ in 1...10 {
    print("learn swift")
}

• while循环

var i = 0
while i != 100 {
    i += 2
}

• continue and break

var i = 0
while true {
    if i == 50 {
        break
    }
    if i == 2 {
        continue
    }
    print("steve yu")
    i += 1
}

for ele in 1...50 {
    if ele == 10 {
        continue
    }
    print("haha")
}

• switch

var choice = 1
switch choice {
case 1:
    print("hahah")
case 10...30:
  	print("20 to 30")
default:
    print("no")
}

8.函数

_是外部变量，如果不加，贼要写变量名

func add(_ x: Int, _ y: Int) -> Int {
    return x + y
}

func prin() {
    print("haha")
}

prin()

add(1, 2)

func minus(c x:Int, d y: Int) -> Int {
    return x - y
}
minus(c: 1, d: 2)

func multi(x:Int, y: Int) -> Int {
    return x * y
}
multi(x: 9, y: 2)

函数参数默认值

func incr(_ num: Int, _ incrNum: Int = 10) -> Int {
    return num + incrNum
}
incr(5)

函数传参

func handle(_ x: Int, _ y: Int, _ method: (Int, Int)->Int) -> Int {
    return method(1, 2)
}

handle(1, 2, add)

闭包

var city = ["shanghai", "hangzhou", "beijing"]
//sorted函数
var cityRank1 = city.sorted()
//函数调用改写
func cmp(a: String, b: String) -> Bool {
    return a < b
}
var cityRank2 = city.sorted(by: cmp)
//闭包改写
var cityRank3 = city.sorted{(a, b) -> Bool in
    return a > b
}
//简写
var cityRank4 = city.sorted{(a, b) in a > b}
//快捷参数
var cityRank5 = city.sorted{$0 > $1}

9.枚举

enum Weather {
    case sunny
    case cloudy
    case rainy
    case snow
    case froggy
}

var todayWeather: Weather = Weather.froggy

switch todayWeather {
case .sunny:
    print("大晴天")
case .froggy:
    print("大雾天")
case .rainy:
    print("下雨天")
case .snow:
    print("大雪天")
case .cloudy:
    print("多云天")
}