swift4 学习笔记(一)

swift4 学习笔记(一)

变量与常量

在swift中用let来表示常量，用var来便是变量

//定义变量
var myVariable = "hello"
//变量的值可以改变
myVariable = "hi"

//定义常量
let myConstantVariable = 123

// 隐式指定整数类型
var anInteger = 2

// 明确指定整数类型
let anExplicitInteger :Int = 2

//定义一个数组
let array = [Any]()

//定义一个字典
let dictionary = [String:Any]()

控制流

for循环

let scoreArray = [10,9,9,2,1,5,6,7]

var totalScore = 0

for i in 0..<scoreArray.count {
    totalScore =+ scoreArray[i]
}

print(totalScore)

if判断语句

if totalScore>50 {
    print("ok")
}else{
    print("not ok")
}

使用if let来处理可能为nil 的赋值,如果下面代码中的optionalName为nil则if判断为否

let optionalName : String? = "jack"
var greeting = "Hello!"

if let name = optionalName {
    greeting = "Hello! \(name)"
}
print(greeting)

??

也可以提供一个默认值来处理optional值为nil的情况
如果下面代码中的nickName为nil时，将会用默认值fullName替代

let nickName:String? = nil
let fullName:String = "John Snow"

let informalGreeting = "Hi,\(nickName ?? fullName)"

print(informalGreeting)

switch

switch支持多重数据格式，不局限于整数

let color = "red"
switch color {
case "blue":
    print("the sky is blue")
case "black","white":
    print("black and white")
case let x where x.hasSuffix("red"):
    print(x)
default:
    print("every color is good")
    
}

for in

可以用for in 来遍历字典中的item

let numberDictionary = [
    "first":[1,4,5,6,7,2,9,11],
    "second":[11,23,32,12,1,3,5],
    "third":[66,2,5,7,17,3]
]
var largetNumber = 0
for (_,numbers) in numberDictionary {
    for number in numbers {
        if largetNumber < number {
            largetNumber = number
        }
    }
}
print(largetNumber)

while

使用while来重复执行代码块，直到到达条件

var n = 2

while n<100 {
    n *= 2
}
print(n)

var m = 2

repeat {
    m *= 2
} while m<100

print(m)