在jquery中将类添加到活动列表项

I have list in foreach loop in Php as like below

<?php 
     $cnt=1;
     foreach ($this->session->userdata('questions') as $row) {
         $i=1;
         foreach($row as $q) {      ?>
           <li id="<?php echo "number-". $q->subjectid."_".$i;?>" onclick="showQuestion('<?php echo "#".$q->subjectid."_".$i;?>');" class="btn bg-primary numbers z-answered"  >
            <?php echo $cnt++;?>
            </li>
            <?php 
            $i++;
         } 
    } 
?>

It will show question numbers from 1 to 100 (assume)

I want When a user will click any question, It will add demo css class to current question How to achieve it.

You can use jQuery for the purpose if you want to:

$(document).ready(function(){
  $('li').click(function(){
    $(this).addClass('demo');
    //code to remove class from rest of the <li>'s
    $(this).siblings().removeClass('demo');
  });
});

You can use jQuery's addClass() method.