PHP array traversal

The most efficient of these three methods is to use the foreach statement to traverse the array. The foreach structure has been introduced since PHP4. It is a statement specially designed for traversing arrays in PHP. It is recommended that everyone use it. Let’s first introduce these methods respectively

There are three commonly used methods for traversing arrays in PHP:
1. Use the for statement to loop through the array;
2. Use the foreach statement to traverse the array;
3 , jointly use list(), each() and while loop to traverse the array.
The most efficient of these three methods is to use the foreach statement to traverse the array. The foreach structure has been introduced since PHP4. It is a statement specially designed for traversing arrays in PHP. It is recommended that everyone use it. Let’s first introduce these methods respectively.

1. Use the for statement to loop through an array
It is worth noting that using the for statement to loop through an array requires that the array traversed must be an index array. There are not only associative arrays but also index arrays in PHP, so the for statement is rarely used in PHP to loop through arrays.
The example code is as follows:

The code is as follows:

<?php 
$arr = array(&#39;http://www.php.cn&#39;,&#39;PHP中文网&#39;,&#39;PHP教程&#39;); 
$num = count($arr); 
for($i=0;$i<$num;++$i){ 
echo $arr[$i].&#39;<br />&#39;; 
} 
?>

Note: In the above example code, we first calculate the number of elements in the array $arr, and then use it in for statement, this is very efficient. Because if it is for($i=0;$iThe output result of the above code is:
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2. Use the foreach statement to traverse the array
There are two ways to use the foreach statement to loop through an array. The first method is the one we use most. The introduction is as follows:
The first way:
foreach(array_expression as $value){
//Loop body
}
Example code:

The code is as follows :

<?php 
$arr = array(&#39;http://www.php.cn&#39;,&#39;PHP中文网&#39;,&#39;PHP教程&#39;); 
foreach($arr as $value){ 
echo $value.&#39;<br />&#39;; 
} 
?>

In each loop, the value of the current element is assigned to the variable $value, and the pointer inside the array is moved back one step. Therefore, the next element of the array will be obtained in the next loop, and the loop will not stop until the end of the array, ending the traversal of the array.

Second way:
foreach(array_expression as $key=>$value){
//Loop body
}
Example code:

The code is as follows:

<?php 
//定义数组 
$arr = array(&#39;http://www.php.cn&#39;,&#39;PHP中文网&#39;,&#39;PHP教程&#39;); 
foreach($arr as $k=>$v){ 
echo $k."=>".$v."<br />"; 
} 
?>

3. Combined use of list(), each() and while loop to traverse the array
each() The function takes an array as a parameter, returns the key/value pair of the current element in the array, and moves the array pointer backward to the position of the next element.
list() function, this is not a real function, it is a language structure of PHP. list() assigns values ​​to a set of variables in one step.

Example code:

The code is as follows:

<?php 
//定义循环的数组 
$arr = array(&#39;website&#39;=>&#39;http://www.php.cn&#39;,&#39;webname&#39;=>&#39;php中文网&#39;) 
while(list($k,$v) = each($arr)){ 
echo $k.&#39;=>&#39;.$v.&#39;<br />&#39;; 
} 
?>

The output result is:
website=>http://www.php. cn
webname=>PHP Programmer

Summary: Among the above three methods of looping through arrays, it is recommended that you use the foreach statement to loop through arrays, which is more efficient.

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