php中foreach的两种使用示例详解分析

foreach()有两种用法：

foreach(array_name as $value) 
{ 
statement; 
}

这里的array_name是你要遍历的数组名，每次循环中，array_name数组的当前元素的值被赋给$value,并且数组内部的下标向下移一 步，也就是下次循环回得到下一个元素。

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

这里跟第一种方法的区别就是多了个$key,也就是除了把当前元素的值赋给$value外，当前元素的键值也会在每次循环中被赋给变量$key。键值可以 是下标值，也可以是字符串。比如book[0]=1中的"0"，book[id]="001"中的"id".
程序实例1：

<?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

/*-------------------------------------------------------------------------*/ 
/* 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

/*-------------------------------------------------------------------------*/ 
/* 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

/*-------------------------------------------------------------------------*/ 
/* 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

/*-------------------------------------------------------------------------*/ 
/* 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

也可以这么用：

$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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