Detailed explanation of php arrays

* An array is an ordered collection of key names and values ​​

* 1. Category:

* [Key name]

* 1.1 Index array [default]: The key name is an integer [it will be automatically converted if not]

* 1.2 Associative array: the key name is a string [can be converted into object properties]

* [Is the key value an array?]

* 1.1 One-dimensional array: The key value is a non-array type, the most commonly used

* 1.1 Multi-dimensional array: The key value is still an array, the most commonly used is a two-dimensional array, nesting is not recommended Too deep

* 2. Create:

* 2.1 Unified creation: $arr = [element1,element2,...];

* 2.2 Create one by one: $arr =[];$arr[]=element1;$arr[]=element2,...

* 3. Access: square brackets plus key name [key]

* 3.1 Overall: print_r($arr); var_dump($arr);

* 3.3 One by one: echo $array[key]: $array['name'];

* 4. Update:

* 4.1 Overall: It needs to be implemented through loop traversal: foreach($arr as $value){//...};

* 4.2 One by one: $arr[key] = new_value;

* 4.3 Clear or rebuild: $arr=[]; $arr = [1,2,3...]; Re-declaring it with the original name will overwrite the original array

* 5. Delete :

* 5.1 Overall: unset($arr);

* 5.2 Single deleted key name without rearrangement: unset($arr[key]);

* 5.3 Single deletion key name rearrangement [for index array]: array_splice($arr,$start,$count,[$newEle]);

* 5.4 Delete null value elements: array_filter($arr);

* 5.5 Delete specific elements: foreach if unset

//1.Create

$city = ['合肥','上海','杭州','南京']; //索引数组
$user = ['id'=>10,'name'=>'Peter','course'=>'php','grade'=>99]; //关联数组

//2.Access

print_r($user);  //整体输出
echo &#39;<hr>&#39;;
echo $user[&#39;name&#39;];  //查看单个元素
echo &#39;<hr>&#39;;

//3.Update

$user['name']='朱老师'; //更新操作
echo $user['name'];  //再次查看

//4.Delete

unset($city);  //删除整个数组
echo &#39;<pre class="brush:php;toolbar:false">&#39;;
print_r($city); //查看不存在的变量会报错,加@符可忽略Notice级错误
echo &#39;<hr>&#39;;
unset($user[&#39;course&#39;]);  //删除单个元素
echo &#39;<pre class="brush:php;toolbar:false">&#39;;
print_r($user);  //整体输出, $user[&#39;course&#39;]元素已经不存在了
echo &#39;<hr>&#39;;
$city = [&#39;合肥&#39;,&#39;上海&#39;,&#39;杭州&#39;,&#39;南京&#39;]; //索引数组
echo &#39;<pre class="brush:php;toolbar:false">&#39;;
print_r($city);  //原始索引数组
echo &#39;<hr>&#39;;
echo &#39;<pre class="brush:php;toolbar:false">&#39;;
//array_splice(arr,start,end,preserve):从数组特定位置取出指定数量的元素
//返回取出的数据,取出的数据从原始数组中删除掉
//从$city的第二个元素开始,取出2个并返回它们
print_r(array_splice($city,1,2)); 
echo &#39;<pre class="brush:php;toolbar:false">&#39;;
//再次查看,会发现取出的元素,已经从原始数组中消失了
print_r($city);  //整体输出