Checkbox post variable/array when there's only one checkbox selected

PHP:

if (isset($_POST['checkbox'])){
    foreach ($_POST['checkbox'] as $x){
        array_push($arr, judgeNametoID($x));
    }
}

I've been getting errors when there's only one checkbox selected. If I keep the isset() in there, I don't get errors, only the checkbox selected is not added to the array.

Why is $_POST['checkbox'] not getting set if there's only one checkbox selected?

PHP/HTML of page with the checkboxes:

echo '<ul>';
            $list = getActiveJudges();
            foreach ($list as $x){
                $found = 0;
                    foreach ($arr as $y){
                        if ($x == $y){
                            $found = 1;
                            break;
                        }
                    }
                    if ($found==1){
                        echo '<li>';
                        array_push($selectedJudges, judgeNametoID($x));
                        echo '<input type="checkbox" checked="checked" name="checkbox[]" value="'.$x.'" />'.$x.'<br/>';
                        echo '</li>';   
                    }
                    开发者_JS百科else {
                        echo '<li>';
                        echo '<input type="checkbox" named="unchecked[]" value="'.$x.'" />'.$x.'<br/>';
                        echo '</li>'; 
                    }
            }
                echo '</ul>';

Errors when I remove the isset():

Notice: Undefined index: checkbox in c:\Inetpub\wwwroot\CaseManagement\changeuserjudgeprocess.php on line 11

Warning: Invalid argument supplied for foreach() in c:\Inetpub\wwwroot\CaseManagement\changeuserjudgeprocess.php on line 14

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Is the input name actually checkbox? If you want to iterate through a list of checkboxes, you'll need html like this

<input type="checkbox" name="checkbox[]">
<input type="checkbox" name="checkbox[]">
<input type="checkbox" name="checkbox[]">

But that doesn't help very much as you won't know which checkbox was checked, so you could try something like

<input type="checkbox" name="checkbox[checkbox1]">
<input type="checkbox" name="checkbox[checkbox2]">
<input type="checkbox" name="checkbox[checkbox3]">

and then loop through like so:

if(isset($_POST['checkbox'])){
    foreach($_POST['checkbox'] as $checkboxID => $checkboxVal){
         // $checkboxID will be checkbox1, checkbox2, checkbox3 as specified above.
         // $checkboxVal will always be 'on'
    }
}

Of course, you may already have html like this, if so, we'll need to see it in order to help more :)

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Maybe what you checked is the checkbox which the name is 'unchecked[]'

By the way, it is not necessary to give the unchecked checkbox a differernt name.