key ( $array );

<?php
   fruit = array(
      'f1' => 'apple',
      'f2' => 'orange',
      'f3' => 'grape',
      'f4' => 'apple',
      'f5' => 'apple');

   while (f_name = current(fruit)) {
      if (f_name == 'apple') {
         echo key(fruit)."\n";
      }
      next(fruit);
   }
?>

f1
f4
f5