PHP - If div has certain class then

My question is simple.

I have the following code:

    <div class="last" 
    <?php 
    if hasClass(last){
      echo " style='width:100%;' ";
    } 
    ?> 
    ></div>

I know the if statement is wrong, but the idea is there. I want to know how can I check if this div has the .last class then echo something.

I've been searching around but didn't work anything (didn't find much though).

Best regards.