concate php variable
<p>When concatenate php variable result not showing.</p>

<pre><code>$a = 5;
$b = 4;
$o = '+';

echo $a.$o.$b;
result showing 5+4; but i want show result 9 
</code></pre>

<p>How can i do this, anybody can help me out. 
Thanks in advance. </p>
