php代码100分,该如何解决

if(!in_array($_POST['type'],array('login','reg'))){
	echo -1;
	exit();
}
if($_POST['type']=='login'){
	$username=addslashes($_POST['username']);
	$pwd=$_POST['pwd'];
	$sql="SELECT * FROM test WHERE name='$username'";//test改为user-info
	$db=new DB();
	if($user_exists=$db->execute_dql($sql)){
		if(md5($pwd)==$user_exists[0]['pwd']){
			session_start();
			$_SESSION['username']=$user_exists[0]['name'];
			echo 1;
			exit();
		}
	}else{
		echo -1;
		exit();
	}
}elseif($_POST['type']=='reg'){
	$username=addslashes($_POST['username']);
	$pwd=md5($_POST['pwd']);
	$sql_exists="SELECT * FROM test WHERE name='$username'";//test改为user-info
	$db=new DB();
	if($db->execute_dql($sql_exists)){//已存在该用户
		echo -2;
		exit();
	}
	$sql="INSERT INTO test(name,pwd) VALUES('$username','$pwd')";//test改为user-info
	if($code=$db->execute_dml($sql)){
		session_start();
		$_SESSION['username']=stripslashes($username);
		echo 1;
		exit();
	}else{
		echo -1;
		exit();
	}
}

class DB{
	private $conn;
	private $host="localhost";//localhost:3307
	private $user="root";
	private $password="123456";
	private $db="test";//bbs
	private $res;

	function __construct(){
		$this->conn=mysql_connect($this->host,$this->user,$this->password);
		if(!$this->conn){
			die("连接数据库失败".mysql_error());
		}
		mysql_select_db($this->db,$this->conn);
		mysql_query("SET NAMES utf8");
	}
	function execute_dql($sql){
		$this->res=mysql_query($sql,$this->conn) or die(mysql_error());
		$r=array();
		while($row=mysql_fetch_assoc($this->res)){
			$r[]=$row;
		}
		return $r;
	}
	function execute_dml($sql){
		$b=mysql_query($sql,$this->conn) or die(mysql_error());
		if(!$b){
			return 0;//失败
		}else{
			if(mysql_affected_rows($this->conn)>0){
				return 1;//成功
			}else{
				return 2;//没有影响到行数
			}
		}
	}
	function __destruct(){
		if(!empty($this->res)){
			mysql_free_result($this->res);
		}
		mysql_close($this->conn);
	}
}

?>

if(!in_array($_POST['type'],array('login','reg'))){
	echo -1;
	exit();
}
if($_POST['type']=='login'){
	$username=addslashes($_POST['username']);
	$pwd=$_POST['pwd'];
	$sql="SELECT * FROM test WHERE name='$username'";//test改为user-info
	$db=new DB();
	if($user_exists=$db->execute_dql($sql)){
		if(md5($pwd)==$user_exists[0]['pwd']){
			session_start();
			$_SESSION['username']=$user_exists[0]['name'];
			echo 1;
			exit();
		}
	}else{
		echo -1;
		exit();
	}
}elseif($_POST['type']=='reg'){
	$username=addslashes($_POST['username']);
	$pwd=md5($_POST['pwd']);
	$sql_exists="SELECT * FROM test WHERE name='$username'";//test改为user-info
	$db=new DB();
	if($db->execute_dql($sql_exists)){//已存在该用户
		echo -2;
		exit();
	}
	$sql="INSERT INTO test(name,pwd) VALUES('$username','$pwd')";//test改为user-info
	if($code=$db->execute_dml($sql)){
		session_start();
		$_SESSION['username']=stripslashes($username);
		echo 1;
		exit();
	}else{
		echo -1;
		exit();
	}
}

class DB{
	private $conn;
	private $host="localhost";//localhost:3307
	private $user="root";
	private $password="123456";
	private $db="test";//bbs
	private $res;

	function __construct(){
		$this->conn=mysql_connect($this->host,$this->user,$this->password);
		if(!$this->conn){
			die("连接数据库失败".mysql_error());
		}
		mysql_select_db($this->db,$this->conn);
		mysql_query("SET NAMES utf8");
	}
	function execute_dql($sql){
		$this->res=mysql_query($sql,$this->conn) or die(mysql_error());
		$r=array();
		while($row=mysql_fetch_assoc($this->res)){
			$r[]=$row;
		}
		return $r;
	}
	function execute_dml($sql){
		$b=mysql_query($sql,$this->conn) or die(mysql_error());
		if(!$b){
			return 0;//失败
		}else{
			if(mysql_affected_rows($this->conn)>0){
				return 1;//成功
			}else{
				return 2;//没有影响到行数
			}
		}
	}
	function __destruct(){
		if(!empty($this->res)){
			mysql_free_result($this->res);
		}
		mysql_close($this->conn);
	}
}

?>