Swift学习笔记（Page.1）

Swift学习笔记（Page.1）

Hello, Swift!

print("Hello, Swift!")

VarsAndConstants

变量（Vars）：

//变量
var a = 1
a = 10
var b = 2

常量（Constants）：

//常量
let c = a+b

//error:
//c = 10

Use let to make a constant and var to make a variable. The value of a constant doesn’t need to be known at compile time, but you must assign it a value exactly once. This means you can use constants to name a value that you determine once but use in many places.

使用 let 来声明常量,使用 var 来声明变量。一个常量的值在编译时并不需要获取，但是你只能为它赋值一次。也就是说你可以用常量来表示这样一个值：你只需要决定一次，但是该值需要使用很多次。

Types

变量在赋值后会自动转化类型，

var str = "Hello"

可以用如下的方法为变量指定类型

var s:String = "World"
var i:Int = 100
var word:String = "Swift"

一般情况下，我们不会指定变量类型，由系统自动指定。

Strings

字符串的拼接

let label = "The width is "
let width = 94
let widthLabel = label + String(width)
//"The width is 94"

let apples = 3
let oranges = 5
let appleSummary = "I have \(apples) apples."
//"I have 3 apples."
let fruitSummary = "I have \(apples + oranges) pieces of fruit."
//"I have 8 pieces of fruit."

ArrayAndDictionary

数组：

初始化一个数组

var array = []

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

指定数组中元素的类型为String

let emptyArray = [String]()
var stringArray:[String] = ["A", "B", "C"]

字典：

初始化一个字典

var dict = [:]

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

指定字典中键（Key）的类型为String，值（Value）的类型为Float

let emptyDictionary = [String: Float]()
var stringDictionary[String:Float] = ["age":18]

Control Flow

For

var arr:[String] = []
for index in 0...9 {
    arr.append("Item \(index)")
}

//for index in 0..<9 {
//    arr.append("Item \(index)")
//}

print(arr)
//["Item 0", "Item 1", "Item 2", "Item 3", "Item 4", "Item 5", "Item 6", "Item 7", "Item 8", "Item 9"]

for value in arr {
    print(value)
}

var dict = ["name":"Swift", "age":18]

for (key, value) in dict {
    print("\(key), \(value)")
}
//age, 18
//name, Swift

While

var n = 2
while n < 100 {
    n = n * 2
}
print(n)
//128

var m = 2
repeat {
    m = m * 2
} while m < 100
print(m)
//128

Switch

let vegetable = "red pepper"
switch vegetable {
    case "celery":
        print("Add some raisins and make ants on a log.")
    case "cucumber", "watercress":
        print("That would make a good tea sandwich.")
    case let x where x.hasSuffix("pepper"):
        print("Is it a spicy \(x)?")
    default:
        print("Everything tastes good in soup.")
}
//"Is it a spicy red pepper?\n"

Flow（控制流）

let individualScores = [75, 43, 103, 87, 12]
var teamScore = 0
for score in individualScores {
    if score > 50 {
        teamScore += 3
    } else {
        teamScore += 1
    }
}
print(teamScore)
//"11\n"