当使用循环检查复选框时，如何显示值？

How can i show value when checkbox was checked using loop for ?

.....................................................................................................................................................................

<form method="post">
    <input type="checkbox" name="a_0" value="0">0
    <input type="checkbox" name="a_1" value="1">1
    <input type="checkbox" name="a_2" value="2">2
    <input type="checkbox" name="a_3" value="3">3
    <input type="checkbox" name="a_4" value="4">4
    <input type="submit" name="submit">
</form>



<?php
    if(isset($_POST["submit"]))
    {
        for($i=0;$i<4;$i++)
        {
            if(${"_POST[a_{$i}]"} != '')
            { echo ${"_POST[a_{$i}]"}; }
            else
            { echo "no"; }
        }
    }
?>

Change:

${"_POST[a_{$i}]"} 

To:

$_POST['a_' . $i]

Or (note the double quotes):

$_POST["a_$i"]

Try like this:

<?php
    if(isset($_POST["submit"]))
    {
        for($i=0;$i<4;$i++)
        {
            if(${"_POST[a_{$i}]"} != '')
            { echo $_POST['a_{$i}']; }
            else
            { echo "no"; }
        }
    }
?>