我怎么能用php发布复选框？

This is my form and categories comes from the database with while loop. I want to insert the checked inputs only in to database.

How can i detect which checkbox is selected ?

<form action="account.php" method="POST">
    <ul class="account-info">
        <li>Category1 : <input type="checkbox" value="val1" name="cat1"></li>
        <li>Category2 : <input type="checkbox" value="val2" name="cat1"></li>
        <li>Category3 : <input type="checkbox" value="val3" name="cat1"></li>
        <!-- while continues -->
        <li>Category100 : <input type="checkbox" value="val100" name="cat1"></li>
    </ul>
    <input type="submit" value="submit" />
</form>

In account.php only the check boxes will be posted. As you've named them all the same though, only 1 will be posted, the last checkbox. If you want them to have the same name and come through as an array you need to add [] after the name, like this:

<input type="checkbox" value="val100" name="cat1[]">

Then in your account.php where they are submitted you can do this:

foreach($_POST['cat1'] as $val)
{
    echo "$val<br>";
}

That will echo out the values of all the checked boxes.

You can check it like that: This code will check which categories are activated assuming that your database returns categories from 0 to x

 $i = 0; 
    while(true){
    if ($_POST["cat".$i."]) {   
        //category activated
    } 
    else { 
        //no category found -> loop ends
        break;
    }
    $i++;
    }

change the name="cat1" to name="cat[1][]"

in your account.php page

foreach($_POST['cat'] as $category){ 
    foreach($category as $value){
        echo $value;
    }
}

First off, you have your options set up as if they were radio buttons all having the same name turning into 1 value out of the 3 possible. If you want them to be conventional checkboxes you have to give them separate names.

in your PHP you would check if the array_key_exists for the checkbox name in question, this is how I usually translate the checkbox fields in a form to be easier to use:

<?php
    $checked = array(
        'cat1' => array_key_exists('cat1', $_POST),
        'cat2' => array_key_exists('cat2', $_POST),
        'cat3' => array_key_exists('cat3', $_POST)
    );
    print_r($checked);
    exit;
?>