The most complete introduction to PHP arrays

This article mainly provides a general introduction to PHP arrays. The language is simple but very comprehensive. I hope that friends who are new to PHP will have a clearer understanding.

1. What is an array?
An array is a collection of data that organizes a series of data to form an operable whole. Each entity of an array contains two items: a key and a value.

2. Declaring data
There are two main ways to declare an array in PHP: one is to declare the array using the array() function, and the other is to directly assign values ​​to the array elements.
<1>The array() function declares the array in the form of array([mixed...]). The syntax of the parameter mixed is key=>value
For example,

<?php
$array=array("1"=>"编","2"=>"程","3"=>"词","4"=>"典");
print_r($array);
echo "<br>";
echo $array[1]; //注意：下标默认是从0开始      
echo $array[2];       
echo $array[3];       
echo $array[4];       
?>

<2> ; Directly assign values ​​to array elements. This method of array creation is better if you don't know the size of the array when you create it, or if the size of the array may change when you actually write the program.
For example,

<?php
$array[1]="I";
$array[2]="love";
$array[3]="PHP";
print_r($array); //输出所创建数组的结构

?>

3. Array type
PHP supports two types of arrays: indexed array and associative array. The former Use numbers as keys, the latter uses strings as keys.

4. Output Array
Outputting array elements in PHP can be achieved through echo and print statements, but this can only output a certain element in the array; to output the array structure, you must Use the print_r() function, its syntax: print_r (mixed expression_r). If the parameter expression_r is an ordinary integer, character or real variable, the variable itself will be output. If the parameter is an array, it will be displayed in the order of a certain key value and element. Get all elements in the array.

5. Array construction
One-dimensional array:
When the elements of an array are variables, it is called a one-dimensional array.
Declare a one-bit array: Type specifier array name [constant expression];
Two-dimensional array:
When the element of an array is a one-bit array, it is called a two-dimensional array.
For example,

<?php
$str = array (
     "网络编程语言"=>array ("PHP","JSP","ASP"),
"体育项目"=>array ("m"=>"足球","n"=>"篮球"));
print_r ( $str) ;
?>

6. Traversing the array
Traversing all the elements in the array is a common operation, and queries or other functions can be completed during the traversal process. There are many ways to traverse an array in PHP. The two most commonly used methods are introduced below.
<1>Use the foreach structure to traverse the array;
<2>Use the list() function to traverse the array. The list() function can only be used for numerically indexed arrays, and the numerical index starts from 0.
Example: Comprehensive use of list() and each() to authenticate user login:

<?php
//输出用户登录信息
while(list($name,$value)=each($_POST)){
if($name!="submit"){
   echo "$name=$value<br>";
}
}

?>
7. Count the number of array elements
In PHP, use count The () function counts the number of elements in the array. The syntax is: int coun(mixed array[,int mode]), where the parameter array is a required parameter and mode is an optional parameter. If COUNT——RECURSIVE(or 1 ), this function will recursively pair arrays of arrays. For example,

<?php
$array = array("php" => array("PHP函数参考大全","PHP程序开发范例宝典","PHP数据库系统开发完全手册"),
               "asp" => array("ASP经验技巧宝典")
         ); //声明一个二维数组       
echo count($array,COUNT_RECURSIVE);//递归统计数组元素的个数，运行结果为6
?>

8. Array sorting
<1> Use sort() and rsort() to perform ascending and descending order of the array respectively, such as,

<?php
$array=array(5,26,37,18,9,42,88,66);
$array1=sort($array);       
for($i=0;$i<count($array);$i++){  
   echo $array[$i]."  ";  
}
echo "<br>";
$array1=rsort($array);      
for($i=0;$i<count($array);$i++){     
echo $array[$i]."  ";
}
?>

Running results:
5 9 18 26 37 42 66 88
88 66 42 37 26 18 9 5
<2>Use ksort() and asort() to sort the associative array
If used After sorting the related array, you need to keep the order of keywords and values ​​consistent. In this case, you need to use the ksort() and asort() functions

, such as,

<?php
$array=array(&#39;php&#39;=>1,&#39;jsp&#39;=>2,&#39;asp&#39;=>3);
ksort($array);
print_r($array);
echo "<br>";
asort($array);
print_r($array);
?>

Run result:
Array ( [asp] => 3 [jsp] => 2 [php] => 1 )
Array ( [php] => 1 [jsp] => 2 [asp] => 3)

The above eight aspects briefly introduce the definition, structure and methods of PHP arrays from the shallower to the deeper. I hope it will be helpful to everyone. Regarding the issue of arrays, the editor More corresponding tutorial articles will be compiled in the future.

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