单纯值：
1.let常量声明，var声明变量（同时宣布福值，编译器会自己主动判断出类型）
var myVariable = 42
myVariable 50
let myConstant = 42
let implicitInteger = 70
let implicitDouble = 70.0
let explicitDouble:Double = 70
声明类型时在“量”后面加上“：”然后写上类型的名字。
（值永远不会隐式转换，须要转换请显示转换“类型（量）”）
更简单的办法将值转换成字符串：（量）
let apples = 3
let oranges = 5
let appleSummary = "I have (apples) apples."
let fruitSummary = "I have (apples + oranges) pieces of fruit"
2.“[]”创建数组和字典，key或者下标取值
var shoppingList = ["catfish","water","tulips","blue paint"]
shoppingList[1] = "bottle of water"
var occupations = ["Malcolm":"Captain","KayLee":"Mechanic"]
occupations["Jayne"] = "Public Relations"
空数组和空字典声明
let emptyArray = String[]()
let emptyDictionary = Dictionary<String,Float>()
假设类型信息能够别判断出来。你能够用[]和[:]来创建空数组和空字典，就想你声明变量或者给函数传递參数的时候一样
shoppingList = []
控制流
1.if,switch进行条件操作。for-in,for,while,do-while进行循环（包裹条件和循环变量括号能够省略。可是语句体的大括号是必须的）
let individualScores = [75,43,103,87,12]
var teamScore = 0
for score in individualScores{
if score>50{
teamScore += 3
}
else
{
teamScore += 1
}
}
if语句的条件必须是布尔值，一个可选的值可能是一个详细的值或者是nil。表示值缺失。在类型后面加上一个问号来标记这个变量的值是可选的。
var optionalString : String? = "Hello"
optionalString == nil
var optionalName:String?="John Appleseed"
var greeting = "Hello!"
if let name = optionalName{
greeting = "Hello, (name)"
}
switch支持随意类型的数据以及各种比較操作
let vegetable = "red pepper"
switch vegetable{
case "celery":
let vegetableComment = "Add some raisins and make ants on a log."
case "cucumber","watercress":
let vegetableComment = "That would make a good tea sandwich."
case let x where x.hasSuffix("pepper"):
let vegetableComment = "Is it a spicy(x)?
"
default:
let vegetableComment = "Everything tastes good in soup."
}
使用for - in 来遍历字典。需呀两个变量来表示每一个键值对
let interestingNumbers = {
"Prime":[2,3,5,7,11,13],
"Fibonacci":[1,1,2,3,5,8],
"Square":[1,4,9,16,25],
]
var largest = 0
for(kind,numbers) in interestingNumbers{
for number in numbers{
if number > largest{
largest = number
}
}
}
largest
var n = 2
while n < 100{
n = n*2
}
var m = 2
do{
m = m*2
}while m < 100
var firstForLoop = 0
for i in 0...3{
firstForLoop += i
}
var secondForLoop = 0
for var i= 0;i < 3;++i{
secondForLoop += 1
}
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