Swift语法备忘录1-Simple Values

这句代码已经是一个完整的程序了

print("Hello World")

let 声明恒量 编译期不需要知道类型，但是必须正确的赋值
var 声明变量

自动类型推断这个恒量的类型，另外，也在冒号后面指定类型

let implicitFloat:Float = 4
print(implicitFloat)

不能含蓄的进行类型转换，需要明确的指定类型

let label = "the width is "
let width = 94
let labelWidth = label + String(width)
print(labelWidth)

拼接不同类型的变量

let oldFloat = 4.0
let Jack = "Jack"
let jackOld = "jack is \(oldFloat) years old"
print(jackOld)

""" 连续的三个双引号表示换行

let apples = 3
let oranges = 5
let quotation = """
I said "I have \(apples) apples."
And then I said "I have \(apples + oranges) pieces of fruit."
"""
print(quotation)

使用圆括号和方括号创建数组和字典([])，使用索引获取或者赋值，允许子啊末尾添加一个逗号

var shoppingList = ["catfish", "water", "tulips", "blue paint"]
print(shoppingList)  ["catfish", "water", "tulips", "blue paint"]
shoppingList[1] = "bottle of water"
print(shoppingList)  ["catfish", "bottle of water", "tulips", "blue paint"]

var occupations = [
    "Malcolm": "Captain",
    "Kaylee": "Mechanic",
]
occupations["Jayne"] = "Public Relations"
print(occupations)

初始化空的数组和字典，需要使用初始化格式

let emptyArrar = [String]()
let emptyDic = [String: Float]()
 如果消息可以推断出来，就不用指定类型了, 比如，给新变量赋值，或者函数传参
shoppingList = []
occupations = [:]
print(shoppingList)
print(occupations)