PHP str_replace

Question

I have the string $var in which I need to replace some text. The first \"X\" needs to be replaced by \"A\", the second \"X\" needs to be replaced by B and so on, here is an exam

Answer 1

Without use of regex

$arr = explode('X', 'X X X X');
$rep = array('A','B','C','D');
foreach ($arr as $idx=>$val)
{
  $arr[$idx] = $val.$rep[$idx];
}
echo implode($arr);