how to mix html and php?

<
I am trying to determine which of these buttons to display based on the num_projects. But the else doesn't seem to work.   
<php if ($this->dataStore("cost_center")->get(0,"num_projects")>0 ;?>
            <button type="button" class="btn btn-success"><i class="fa fa-star"></i>  1. Company</button>
        else
            <button type="button" class="btn btn-danger"><i class="fa fa-star"></i>  1. Company</button>

proof that an old dog can learn new tricks