Swift的基本知识(一)

1、常量与变量的定义

在swift中，常量的命名用let关键字来创建，变量的命名用关键字var来创建

  //常量的命名        let name = "HelloWorld"        print("常量是：\(name)")        //变量的命名        var nickName = String()        nickName = "Bird"        print("变量是：\(nickName)")

输出：

常量是：HelloWorld
变量是：Bird

2、字符串串接及类型转换

在swift中，支持“＋”运算符，用它可以对两个字符串进行连接

   let label = "the width is "        let width = 94        let widthLabel = label + String(width);        print(widthLabel);

输出：

the width is 94

3、数组和字典

在swift中，数组和字典都使用“［］”中括符，并且可以通过索引或key／value的方式存储。

  //数组        var array = ["d","df","cs","ea","fees"]        print(array)        //利用索引对数组进行修改        array[1] = "ABC"        print(array)

 输出：

["d", "df", "cs", "ea", "fees"]
["d", "ABC", "cs", "ea", “fees”]

 // 字典        var dictionary = [String:String]();        dictionary["adc"] = "ADC"        dictionary["aaa"] = "AAA"        print(dictionary)

输出：

["aaa": "AAA", "adc": “ADC”]

//数组中的增删改查        var arr = ["a","b","c","d","e","f"]           //增加某个元素        arr.append("AA")        print(arr)        arr.append(contentsOf: ["1","2","3"])        print(arr)        arr.insert("ABC", at: 5)        print(arr)        arr.insert(contentsOf: ["AAAAA","BBBBB","CCCCC"], at: 3)        print(arr)        //删除序号处的元素        arr.remove(at: 2)        print(arr)        //全部删除        arr.removeAll()        print(arr)        //改        arr = ["ABC","ABD","ABF","ABE","ABG","ABH"]        print(arr)        arr[2] = "11111"        print(arr)        arr.replaceSubrange(1...3, with: ["222","333","444","555"])        print(arr)        arr.replaceSubrange(1...3, with: ["BMW"])        print(arr)        //数组的长度        print(arr.count)        //遍历数组        for ele in arr{            print(ele)        }

输出：

["a", "b", "c", "d", "e", "f", "AA"]
["a", "b", "c", "d", "e", "f", "AA", "1", "2", "3"]
["a", "b", "c", "d", "e", "ABC", "f", "AA", "1", "2", "3"]
["a", "b", "c", "AAAAA", "BBBBB", "CCCCC", "d", "e", "ABC", "f", "AA", "1", "2", "3"]
["a", "b", "AAAAA", "BBBBB", "CCCCC", "d", "e", "ABC", "f", "AA", "1", "2", "3"]
[]
["ABC", "ABD", "ABF", "ABE", "ABG", "ABH"]
["ABC", "ABD", "11111", "ABE", "ABG", "ABH"]
["ABC", "222", "333", "444", "555", "ABG", "ABH"]
["ABC", "BMW", "555", "ABG", "ABH"]
5
ABC
BMW
555
ABG
ABH

  //swift中字典的运用        var dict : [String:String] = ["a":"1","b":"2"]        //添加        dict["c"] = "3"        print(dict)        dict["c"] = "333"        print(dict)                dict .removeValue(forKey: "c")        print(dict)                dict.updateValue("AAAAA", forKey: "a")        print(dict)        let abc = Array(dict.keys)        let abc1 = Array(dict.values)        print("\(abc)==\(abc1)");

输出：

["b": "2", "a": "1", "c": "3"]
["b": "2", "a": "1", "c": "333"]
["b": "2", "a": "1"]
["b": "2", "a": "AAAAA"]
["b", "a"]==["2", “AAAAA”]