Swift 一 基础 The Basic

• 声明常量和变量

let maximumNumberOfLoginAttempts = 10
var currentLoginAttempt = 0

• 在一行中声明多个常量或者多个变量

var x = 0.0,y = 0.0, z = 0.0

• 类型注解

var welcomeMessage:String
welcomeMessage = "Hello"
var friendlyWelcome = "Hello!"
friendlyWelcome = "Bonjour!"

• 整数

let minValue = UInt8.min
let maxValue = UInt8.max
let decimalInteger = 17
let binaryInteger = 0b10001 // 二进制17
let octalInteger = 0o21 // 八进制17
let hexadecimalInteger = 0x11 // 十六进制17

• 推断Double类型，优先使用Double

let 兀 = 3.14159

• 指数

let exp = 1.25e2 //  125
let expf = 1.25e-2 // 0.0125

• 整数和浮点数转换

let three = 3
let pointOneFourOneFiveNine = 0.14159
let pi = Double(three) + pointOneFourOneFiveNine
let integerPi = Int(pi)

• 类型别名

typealias AudioSample = UInt16
var maxAmplitudeFound = AudioSample.max

• Boolean

let orangesAreOrange = true
let turnipsAreDelicious = false
if turnipsAreDelicious {
    print("呃")
} else {
    print("哈哈")
}

• 元组

let http404Error = (404,"Not Found")
let (statusCode,statusMessage) = http404Error
print("The status code is \(statusCode)")
print("The status message is \(statusMessage)")
let http200Status = (statusCode:200,description:"OK")
print("The status code is \(http200Status.statusCode)")
print("The status message is \(http200Status.description)")

• 可选类型

var serverResponseCode:Int?
if serverResponseCode != nil {
    print("serverResponseCode 不为nil")
}