php - Prepare statement filling -

so i'm trying make 1 class (for mysqli operations) reusable other classes (which use different tables , parameters) possible. fragment main class:

class sql {     private $sql;     public function __construct()     {         $this->sql = new mysqli(db_host, db_user, db_password, db_database);         if ($this->sql->connect_errno > 0)         {             die('unable connect database: ' .$this->sql->connect_error);         }         elseif (!$this->sql->set_charset("utf8"))         {             printf('error loading character set utf8: ' .$this->sql->error);         }     }     public function newentry($table, $entrystring, $valuestring, $typestring, $datastring)     {         $statement = $this->sql->prepare("insert $table($entrystring) values ($valuestring)");         $statement->bind_param($typestring, $datastring);         $statement->execute();         $statement->close();         $this->sql->close();     } } 

and here other class, in i'm trying pass variables main function newentry():

class user extends sql {     protected $table = 'foo';      public function newuser($name, $surname)     {         $entrystring = 'name, surname';         $valuestring = '?, ?';         $typestring = 'ss';         $datastring = '$name, $surname';         parent::newentry($this->table, $entrystring, $valuestring, $typestring, $datastring);     } } 

so when i'm trying execute this, "warning: mysqli_stmt::bind_param(): number of elements in type definition string doesn't match number of bind variables in..". understand it's because $datastring acts single entry: "john, doe". there way make act numerous separate params instead of string?