php foreach为关键，每两个数字作为一个组

<?php
$data=array('1','2','3','4','5','6','7','8','9','10','11');
foreach($data as $key=> $element){
    if($key % 2 != 0){
        echo $element.'<br />';
    }
    echo '<hr />';
}
?>

php foreach as key, how to make every two number as a group?

I want to output:

1,2
_____
3,4
_____
5,6
_____
7,8
_____
9,10
_____
11

Have a look at the array_chunk() function.

In your case you'd use it like this:

foreach(array_chunk($data, 2) as $values) {
    echo implode(',', $values)."
";
}

During the last iteration $values will have only one element so if you plan to access the elements directly using their index remember to use count() to check the array's element count.

Your foreach() is fine but you want to print every element, not just every even one. You also don't want the horizontal rule every time either, just every even. Thus:

<?php
$data=array('1','2','3','4','5','6','7','8','9','10','11');
foreach($data as $key=> $element){
    echo $element;
    if($key % 2 != 0){
        echo "<br/><hr />";
    }
    else {
        echo ",";
    }
}
?>