未选择值时如何防止按钮提交表单。 不使用JavaScript

Question

Is there anyway of preventing buttons from submitting forms when the value is not selected, without using javascript?

Here is my code.

<!-- form -->
<form name="aform" action="second_page.php" method="POST">
    <div id="collegelane">
         Please choose only one from the following rooms:
    </div>

    <?php

         // connects to database
         require("user_connection.php");


         $q = mysqli_query($connect, "SELECT * FROM `campus`");
         while ($line = mysqli_fetch_assoc($q)) {
         echo '<input id="onclick" type="checkbox" name="car" 
            value="'.$line['room'].'"><label>'.$line['room'].'</label></br>';
        }

    ?>

    </br>
    </br>

    <div id="next">
        <input type="submit" name="next" Value="next"/>
    </div>

</form>

Answer 1

as it has already been suggested add a 'required' attribute on your checkbox as follows, it should work. Not sure about browser support for that attribute, i suspect it might not work on some version of IE.

<?php

             // connects to database
             require("user_connection.php");


             $q = mysqli_query($connect, "SELECT * FROM `campus`");
             while ($line = mysqli_fetch_assoc($q)) {
             echo '<input id="onclick" required type="checkbox" name="car" 
                value="'.$line['room'].'"><label>'.$line['room'].'</label></br>';
            }

        ?>

Answer 2

html5 form validation: http://www.the-art-of-web.com/html/html5-form-validation/

AngularJs form validation: https://docs.angularjs.org/guide/forms