SWIFT学习笔记（1）----- 简单值声明 Sample Values

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1.简单值声明 Sample Values

var myConstant =42 ----------可变值

let myVariable = 42 ------------常量值 “value of a constant doesn’t need to be known at compile time, but you must assign it a value exactly once.”编译前就已经被“知道”，必须给一个确定值
let implicitInteger = 70
let implicitDouble = 70.0
let explicitDouble: Double = 70 Double 为声明数据类型（当不声明数据类型的时候，编译器自动判断数据类型）

声明的变量不能自动转化数据类型，当要转换数据类型时需要用数据类型() 来进行声明转换例如：

let label = "The width is “
let width = 94
let widthLabel = label + String(width) 字符串可以相加？！有木有

在字符串中用 \( ) 来声明是类型转换这里代替了OC 和C 的 %d,%s 等
let apples = 3
let oranges = 5
let appleSummary = "I have \(apples) apples."
let fruitSummary = "I have \(apples + oranges) pieces of fruit. 注意：这里可以直接在字符转中运算

数组，及字典声明

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

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

空数组和空字典

var emptyArray = String[]()

var emptyDictionary = Dictionary<String, Float>()

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