What is the usage of Php array

Php array usage: An array is a collection of data, which organizes a series of data to form an operable whole. You can use the [array()] function to declare an array, and you can directly assign values ​​to array elements.

1. What is an array

An array is a collection of data that organizes a series of data. form an operational 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 an array using the array() function,

One is to directly assign values ​​to array elements.

<1>array() function declares an 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>Assign values ​​to array elements directly.

If you do not know the size of the array when you create it, or the size of the array may change when you actually write the program, it is better to use this method of array creation.

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 uses numbers as keys, and 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 be done on a certain element in the array. Output; to output the array structure, use the print_r() function, its syntax: print_r (mixed expression), if the parameter expression is an ordinary integer, character or real variable, the variable itself will be output. If the parameter is an array, then Displays all elements in the array in the order of a certain key value and elements.

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. During the traversal process, you can Complete a query or other function. 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 Start 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 the count() function to count the number of elements in the array, the syntax is: int coun(mixed array[,int mode]), where the parameter array is a required parameter, mode is an optional parameter, if COUNT——RECURSIVE is selected (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 sort the array in ascending and descending order 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]." ";                                                                                             
}
?>
运行结果：
5 9 18 26 37 42 66 88 
88 66 42 37 26 18 9 5

<2>Use ksort() and asort() to sort associative arrays

If you use associative arrays, you must keep the keys and values ​​sorted consistently after sorting. This is necessary 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);
?>
运行结果：
Array ( [asp] => 3 [jsp] => 2 [php] => 1 ) 
Array ( [php] => 1 [jsp] => 2 [asp] => 3 )

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