swift基础

曾经终败给现在 2022-08-24 00:45 161阅读 0赞

//var变量 let常量 常量不能更改
    var myVariable  = 42
    let myConstant = 43
    //常量不能改变
    //cannot assign to 'let' value 'myConstant'
    //myConstant = 44
    
    
    let label = "hello world is"
    let width = 1
    
    //值永远不会被隐式转换为其他类型。如果你需要把一个值转换成其他类型,请显式转换。
    //Could not find an overload for '+' that accepts the supplied arguments
    //let widthLabel = label + width
    //以下正确
    let widthLabel = label + String(width)
    
    let apples = 3
    let oranges = 5
    let appleSummary = "I hava \(apples) apples."
    let fruitSummary = "I hava \(apples + oranges) fruit"
    println(String(fruitSummary))
    
    //使用方括号[]来创建数组和字典,并使用下标或者键(key)来访问元素。
    var weather = ["spring", "summer", "autumn", "winter"]
    weather[1] = "what"
    var occupations = ["Malcolm": "Captain","Kaylee": "Mechanic",]
    occupations["Jayne"] = "Public Relations"
    
    //要创建一个空数组或者字典,使用初始化语法。
    let emptyArray = String[]()
    let emptyDictionary = Dictionary<String, Float>()

截图：

![20140618155332812][]

let arrayScore = [32, 323, 232, 232]
    var teamScore = 0
    for score in arrayScore {
        if score > 50 {
            teamScore += 3
        } else {
            teamScore += 1
        }
        
    }
    teamScore
    
    var optionalString: String? = "Hello"
    optionalString == nil
    
    var optionalName: String? = "John apple"
    optionalName = nil
    var greeting = "hello!"
    //如果变量的可选值是 nil,条件会判断为 false,大括号中的代码会被跳过。如果不是 nil,会 将值赋给 let 后面的常量,这样代码块中就可以使用这个值了。
    if let name = optionalName {
        greeting = "Hello,\(name)"
    } else {
        greeting = "what the heal"
    }
    
    //switch 支持任意类型的数据以及各种比较操作——不仅仅是整数以及测试相等。
    //运行 switch 中匹配到的子句之后,程序会退出 switch 语句,并不会继续向下运行,所以不 需要在每个子句结尾写 break。
    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."
    }

截图：

![20140618155407953][]

[20140618155332812]: /images/20220823/126059be399740acb597f03326935662.png
[20140618155407953]: /images/20220823/4778887697e04f278c68edfe4ca61d62.png