function foo($a, $b, $c='hello', $d='world') {
  echo $c;
}

i'd like to use
foo('a', 'b', NULL, 'c');
or even better
foo('a', 'b', , 'c');
to have it echo 'hello', the default value.

i have to workaround using 
function foo($a, $b, $c='hello', $d='world') {
  if (is_null($c)) $c = 'hello';
  echo $c;
}

is there a better way? i really miss this vb-feature.

greetings
fab