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  • Swift 学习笔记第一天-变量常量,及数据类型

    1.定义变量

     用关键字 var

    比如 var i=2

    2.定义常量用let

     如let c=3

     可见Swift 定义时不用指定类型。由编译器推断

      如果想指定类型

     var i:Int32=2

     练习

    let apples=3

    var h:Int32=32

    h=32

    let cs="i love (apples + h)as"

    cs 得结果

    会发现程序报错。a

    could not find member ''convertfromstringInterpolationSegment"

     由此可见Swift  会将默认将类型推断为双精度

    正确程序为

    let apples:Int32=3

    var h:Int32=32

    h=32

    let cs="i love (apples + h)as"

    2 .定义数组

      

    var shoppingList=["haha","as",3,32.00]

    可见数组中得元素类型可以不同。

    将数组元素赋给定义得一个变量

    var s= shoppingList[0]


    会发现报错
    错误如下
    prefix /postfix=is reserved
    这个错误我开始以后是var只能定义值类型得原因
    google才发现很有意思得一个错误

    2down voteaccepted

    Add a space after the =. (=[ looks too sad to be an operator.) It's probably seeing =value as a use of a (possible, but not implemented) prefix operator.

    Swift isn't entirely whitespace-agnostic like C... in particular, it uses whitespace to distinguish prefix from postfix operators (because ++i++ in C is a grammar oddity). But it's not ridiculously strict about whitespace like Python either.

     =号前后空格是有一侧存在得是保留运算附

    修改为

    var s:String=shoppingList[0]

    会发现报错

    anyObject is not  转换成string 

    可见数组是指针引用类型

    正确写法是

    var s:String=shoppingList[0] asNSString

    定义字典

    var occupations=[

        "Malcolm": "Captain",

        "Kaylee": "Mechanic",

    ]

    occupations["Jayne"] = "Public Relations"

    把字典中value得类型变化下

    var occupations=[

        "Malcolm": "Captain",

        "Kaylee": 2,

    ]

    occupations["Jayne"] = "Public Relations"

    会发现报错

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  • 原文地址:https://www.cnblogs.com/zhang888/p/3776895.html
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