Swift 学习笔记
发布时间:2020-12-14 02:37:31 所属栏目:百科 来源:网络整理
导读:感谢Github上The Swift Programming Language开源翻译的中文版,感谢极客学院wiki提供的PDF版本 SwiftTour是对Swift主要的语言特性有个速览,后续的教程会逐个展开阐述。 代码上传至Github,有兴趣的可以下载下来试试 import UIKit var str = "Hello,World!"
感谢Github上The Swift Programming Language开源翻译的中文版,感谢极客学院wiki提供的PDF版本 import UIKit
var str = "Hello,World!"
print(str)
// 变量用var声明,常量用let声明,变量类型自动推断
// 可在变量后声明类型,用冒号分隔
var myVariable = 42
let myConstant = 42
myVariable = 50
let explictDouble: Double = 60
// 值永远不会被隐式转换为其他类型,需要转换必须采用显式转换
let label = "The width is "
let width = 94
let widthLabel = label + String(width)
更为常见的将值转换为字符串的方法let apples = 3
let oranges = 5
let appleSummary = "I have (apples) apples"
let fruitSummary = "I have (apples + oranges) pieces of fruit"
[]用来创建数组或字典var shoppingList = ["catfish","water","tulips","blue paint"]
shoppingList[1] = "bottle of water"
var occupations = [
"Malcolm": "Captain","Kaylee": "Mechanic"
]
occupations["Jayne"] = "Public Relations"
创建一个空数组或者字典let emptyArray1 = [String]()
let emptyDictionary1 = [String: Float]()
let emptyArray2: [String] = []
let emptyDictionary2: [String: Float] = [:]
控制流,if和switch用于选择,for-in,for,while和repeat-while用于循环let individualScores = [75,43,103,87,12]
var teamScore = 0
for score in individualScores {
if score > 50 {
teamScore += 3
} else {
teamScore += 1
}
}
print(teamScore)
隐式// 由于不支持隐式转换,条件必须是一个布尔表达式
// 一般采用可选值配合if和let,处理值缺失判断
var optionalString: String? = "Hello"
print(optionalString == nil)
var optionalName: String? = "John Appleseed"
var greeting = "Hello"
if let name = optionalName {
greeting = "Hello,(name)"
}
Switch支持任意类型的数据以及各种比较操作let vegetable = "red pepper"
switch vegetable {
case "celery" :
print("Add some raisins and make ants on a log")
case "cucumber","watercress" :
print("That woould 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")
}
使用for-in遍历字典// 使用for-in遍历字典
let interestingNumbers = [
"Prime": [2,3,5,7,11,13],"Fibonacci": [1,1,2,8],"Square": [1,4,9,16,25],]
var largest = 0
var numberGroup: String = "Null"
for (kind,numbers) in interestingNumbers {
for number in numbers {
if number > largest {
largest = number
numberGroup = kind
}
}
}
print(numberGroup,largest)
while循环// while循环
var n = 2
while n < 100 {
n = n * 2
}
print(n)
var m = 2
repeat {
m = m * 2
} while m < 100
print(m)
可以在循环中使用..<来表示范围,包含上界使用…var firstForLoop = 0
for i in 0..<4 {
firstForLoop += i
}
print(firstForLoop)
var secondForLoop = 0
for var i = 0; i < 4; ++i {
secondForLoop += i
}
print(secondForLoop)
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