Difference between if(isset($var)) and if($var)
<blockquote>
  <p><strong>Possible Duplicate:</strong><br>
  <a href="http://stackoverflow.com/questions/5164972/whats-the-difference-between-ifvariable-and-ifissetvariable">Whats the difference between if(!Variable) and if(isset($variable)) ?</a>  </p>
</blockquote>



<p>In Facebooks php API example they use if($var){ //do something }else{ //do something else}
whick got me thinking about the difference of if($var) and if(isset($var)). The first sure looks neater but can I surely use it?</p>
