I followed the instructions, but all I get is b...

 
function str_ireplace($needle, $replacement, $haystack) { 
$i = 0; 
while (($pos = strpos(strtolower($haystack),strtolower($needle), $i)) !== false) { 
$haystack = substr($haystack, 0, $pos).$replacement.substr($haystack, $pos+strlen($needle));
$i=$pos+strlen($replacement); 
} 
return $haystack; 
}