PHP uses foreach to traverse arrays more efficiently

PHP uses foreach to traverse arrays more efficiently_PHP tutorial

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Release： 2016-07-13 10:32:59

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foreach() has two uses:

foreach(array_name as $value)    
{       
	statement;    
}

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The array_name here is the name of the array you want to traverse. In each loop, the value of the current element of the array_name array is assigned to $value, and the subscript inside the array moves down one step, which is what you get back in the next loop. The next element.

foreach(array_name as $key => $value)    
{        
	statement;      
}

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The difference between this and the first method is that there is an extra $key, that is, in addition to assigning the value of the current element to $value, the key value of the current element will also be assigned to the variable $key in each loop. . The key value can be a subscript value or a string. For example, "0" in book[0]=1, "id" in book[id]="001".

Program example:

<?php
/*-------------------------------------------------------------------------*/
/* foreach example 1: value only */
echo "foreach example 1: value only ".'<br />';
$a = array(1, 2, 3, 17);
foreach ($a as $v) {
   echo "Current value of ".$a.":". $v."<br />";
}
?>
// 运行结果
foreach example 1: value only 
Current value of $a: 1
Current value of $a: 2
Current value of $a: 3
Current value of $a: 17

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/*-------------------------------------------------------------------------*/
/* foreach example 2: value (with key printed for illustration) */
echo '<br />'.'<br />'."foreach example 2: value (with key printed for illustration) ".'<br />';
$a = array(1, 2, 3, 17);
$i = 0; /* for illustrative purposes only */
foreach ($a as $v) {
    echo ""$a[$i] => $v".'<br />';
    $i++;
}
// 程序运行结果
foreach example 2: value (with key printed for illustration) 
$a[0] => 1
$a[1] => 2
$a[2] => 3
$a[3] => 17

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/*-------------------------------------------------------------------------*/
/* foreach example 3: key and value */
echo '<br />'.'<br />'."foreach example 3: key and value ".'<br />';
$a = array(
    "one" => 1,
    "two" => 2,
    "three" => 3,
    "seventeen" => 17
);
foreach ($a as $k => $v) {
    echo ""$a[$k] => $v".'<br />';
}
// 程序运行结果
foreach example 3: key and value 
$a[one] => 1
$a[two] => 2
$a[three] => 3
$a[seventeen] => 17

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/*-------------------------------------------------------------------------*/
/* foreach example 4: multi-dimensional arrays */
echo '<br />'.'<br />'."foreach example 4: multi-dimensional arrays ".'<br />';
$a = array();
$a[0][0] = "a";
$a[0][1] = "b";
$a[1][0] = "y";
$a[1][1] = "z";
foreach ($a as $v1) {
    foreach ($v1 as $v2) {
        echo "$v2"n";
    }
}
// 程序运行结果
foreach example 4: multi-dimensional arrays 
a b y z

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/*-------------------------------------------------------------------------*/
/* foreach example 5: dynamic arrays */
echo '<br />'.'<br />'."foreach example 5: dynamic arrays ".'<br />';
foreach (array(1, 2, 3, 4, 5) as $v) {
    echo "$v"n";
}
// 程序运行结果
foreach example 5: dynamic arrays 
1 2 3 4 5

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can also be used like this:

$messageNav['首页'] =ROOT_PATH;
$messageNav['人才交流'] ="#"
$messageNav['动态专栏'] ="hragent/cn/"
<?php $i = 0;foreach ($messageNav as $key=>$value):?>
<?php if ($i != count($messageNav) - 1):?>
<a href="<?=$value?>"><?=$key?></a>> 
<?php else:?>
<a href="<?=$value?>" class="onlink"><?=$key?></a>
<?php endif;?>
<?php $i++;endforeach;?>

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