title: What is += used for?
body: <p>I think this is a dumb question but I could not find it on php. Why is a + with the = in the following code:</p>
  
  <pre><code>function calculateRanking()
  {
      $created = $this-&gt;getCreated();
  
      $diff = $this-&gt;getTimeDifference($created, date('F d, Y h:i:s A'));
  
      $time = $diff['days'] * 24;
      $time += $diff['hours'];
      $time += ($diff['minutes'] / 60);
      $time += (($diff['seconds'] / 60)/60);
  
      $base = $time + 2;        
  
      $this-&gt;ranking = ($this-&gt;points - 1) / pow($base, 1.5);
  
      $this-&gt;save();
  }
  </code></pre>
  
  <p>Is this so $time has all those values or rather it is adding all the values to $time?</p>
  
  <p>Thanks</p>