<?php
function firstUpper($str){
	$len=strlen($str)-1;
	$firstupper[0]=strtoupper($str[0]);
	$k=1;
	for($i=1;$i<=$len;$i++){
		if($str[$i]=='_'){
			$firstupper[$k++]=strtoupper($str[$i+1]);
			$i++;
		}
		else{
			$firstupper[$k++]=$str[$i];
		}
	}
	$fu=implode("",$firstupper);
	return $fu;
}
$string1="open_door";
$string2="make_by_id";
print_r(firstUpper($string1));
echo "<br/>";
print_r(firstUpper($string2));
?>