Swift学习（1）

swif（1）

println("Hello, world")

输出结果：

Hello, world

---

swift使用let来声明常量，使用var来声明变量

//变量
var myVariable = 42
myVariable = 50
//常量
let myConstant = 42

如果初始值没有提供足够的信息（或者没有初始值），那你需要在变量后面声明类型，用冒号分割

let implicitInteger = 70
let implicitDouble = 70.0
//此处声明explicitDouble是double类型的常量
let explicitDouble: Double = 70

---

类型转换

let label = "The width is"
let width = 94
//嘿嘿，很类似java的强制类型转换
let widthLabel = label + String(width)

---

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

---

swift数组：

1. 类似java数组

   var shoppingList = ["catfish", "water",        "tulips", "blue paint"]
   shoppingList[0] = "catfish"
   shoppingList[1] = "water"
   shoppingList[2] = "tulips"
   shoppingList[3] = "blue paint"
   

2. 或者使用下标或者键（key）来访问元素
   
   var occupations = [
   
   "Malcolm": "Captain",
   
   "Kaylee": "Mechanic",
   
   ]
   
   occupations["Jayne"] = "Public Relations"

3. swift空数组
   
   let emptyArray = String
   
   let emptyDictionary = Dictionary<String, Float>()

---

控制流

java中常见的if..else{...},while,do ...while...,for...在swift中是如何表示的，请往下看：

在数组[75, 43, 103, 87, 12],如果数组中的内容>50,

teamScore+3;否则teamScore+1；

let individualScores = [75, 43, 103, 87, 12]
var teamScore = 0
for score in individualScores {
if score > 50 {
    teamScore += 3
} else {
    teamScore += 1
}
}
teamScore

---

switch语句：

let vegetable = "red pepper"
switch vegetable {
//vegetable=celery的话
case "celery":
let vegetableComment = "Add some raisins and make ants on a log."
//vegetable=celery的话或者watercress
case "cucumber", "watercress":
let vegetableComment = "That would make a good tea sandwich."
//字符串中有pepper话执行
case let x where x.hasSuffix("pepper"):
let vegetableComment = "Is it a spicy \(x)?"
//上面条件都不符合，执行如下代码
default:
let vegetableComment = "Everything tastes good in soup."
}

let anotherCharacter: Character = "a"
switch anotherCharacter {
case "a":
println("The letter a")
case "A":
println("The letter A")
default:
println("Not the letter A")
}

---

（没看懂，）

 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

---

while和do while

swift的循环相比java看起来好奇葩

1. 列表项

初始值为2，便利100以内的值，n=100以内的值逐个*2递增

var n = 2
while n < 100 {
n = n * 2
}
n

var m = 2
do {
m = m * 2
} while m < 100
m

1. 0->3的求和操作，初始值为0

   var firstForLoop = 0
   
   for i in 0..3 {
   
   firstForLoop += i
   
   }
   
   firstForLoop

   var secondForLoop = 0
   
   for var i = 0; i < 3; ++i {
   
   secondForLoop += 1
   
   }
   
   secondForLoop

---

明日计划：

看函数和闭包