php preg replace array

[jman11]

how do you replace a value with an array of values several times?

[JohnCanyon]

$find_array = array('foo','bar');
$replace_array = array('moo','car');

$string = 'foo bar';
echo str_replace($find_array, $replace_array, $string);

//outputs
moo car

[jman11]

everyone does replace with both find an array and the replace an array. how do you do it with just the replace an array?

[JohnCanyon]

Because, the occurance of the first element in the replace array would overwrite all occurances of the find making the additional replaces irrelevant.