title: callback function return return($var & 1)?
body: <p>I have read the PHP Manuel about <a href="http://php.net/manual/en/function.array-filter.php" rel="nofollow">array_filter</a></p>
  
  <pre><code>&lt;?php
  function odd($var)
  {
      // returns whether the input integer is odd
      return($var &amp; 1);
  }
  
  function even($var)
  {
      // returns whether the input integer is even
      return(!($var &amp; 1));
  }
  
  $array1 = array("a"=&gt;1, "b"=&gt;2, "c"=&gt;3, "d"=&gt;4, "e"=&gt;5);
  $array2 = array(6, 7, 8, 9, 10, 11, 12);
  
  echo "Odd :\n";
  print_r(array_filter($array1, "odd"));
  echo "Even:\n";
  print_r(array_filter($array2, "even"));
  ?&gt;
  </code></pre>
  
  <p>Even I see the result here :</p>
  
  <pre><code>Odd :
  Array
  (
      [a] =&gt; 1
      [c] =&gt; 3
      [e] =&gt; 5
  )
  Even:
  Array
  (
      [0] =&gt; 6
      [2] =&gt; 8
      [4] =&gt; 10
      [6] =&gt; 12
  )
  </code></pre>
  
  <p>But I did not understand about this line: <code>return($var &amp; 1);</code> Could anyone explain me about this?</p>