基础知识四：数组

数组（Arrays）是有序数据的集,元素可重复；
遵守Array<Element>类型，Element是这个数组中唯一允许存在的数据类型;
也可以用简单的形式表示:[Element]

1.定义

//空数组
var tempArr = Array<String>() //也可以
var arr = [String]()
//字面量赋值
var arr1 : [String] = ["a","b","c"]
var arr2 = ["a","b","c","d"]

var arr3 = Array(repeating: "0", count: 5)

2.数组是否为空

/*
var arr = [String]()
if arr.isEmpty {
    print("arr is empty")
}
//arr is empty
*/

3.数组的长度：count

4.数组的访问：下标法

var arr2 = ["a","b","c","d"]
print(arr2[2])  //c

5.增

var arr2 = ["a","b","c","d"]
var arr3 = arr2
//增加单个元素
arr2.append("f")
//增加数组
arr2 += ["1","2"]
print(arr2) // ["a", "b", "c", "d", "f", "1", "2"]

arr3.insert("_", at: 0)
print(arr3) // ["_", "a", "b", "c", "d"]

6.删

//tempArr.removeAll() //清空全部数组
//tempArr.removeLast() //删除第一个元素
//tempArr.removeFirst()//删除第一个元素
//tempArr.removeFirst(n: Int) param:n: Int代表第几个元素；n = 1，表示删除tempArr[0]

 var arr2 = ["a","b","c","d"]
 arr2.remove(at: 1)
 print(a)   // ["a", "c", "d"]

7.改

var arr2 = ["a","b","c","d"]
//当个元素
arr2[0] = "1"
print(arr2) //["1", "b", "c", "d"]
//多个元素
arr2[1...2] = ["2","3"]
print(arr2) //["1", "2", "3", "d"]

8.数组的遍历

//forin 遍历 :获取元素
    var arr2 = ["a","b","c","d"]
    for item in arr2 {
        print(item)
    }
//a
//b
//c
//d

//enumerated()遍历，获取每个数据项的值和索引值
    var arr2 = ["a","b","c","d"]
    for (index,value) in arr2.enumerated() {
        print("Item \(String(index)): \(value)")
    }
//Item 0: a
//Item 1: b
//Item 2: c
//Item 3: d