title: php array_filter function not found or invalid function name regardless of what I enter
body: <p>I've never used the array_filter function before so giving it a go by no matter what I use as the function name it is giving me the error</p>
  
  <pre><code>Warning: array_filter() expects parameter 2 to be a valid callback, function 'odd' not found or invalid function name in
  </code></pre>
  
  <p>I have even taken the steps of copying paste the example directly off the php manual page and it is giving me that same error. Code:</p>
  
  <pre><code>function odd($var) {
      // returns whether the input integer is odd
      return($var &amp; 1);
   }
  
  function calculate($res, $period, $elements, $per, $total, $brand = false) {
  
      $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"));
  }
  </code></pre>
  
  <p>I really don't know where to go here. Usually when I'm having trouble I can copy and paste the code exact off the php manual page and work my way back from there but if their example isn't even working it makes it hard.</p>