It must be like this:
//connect
$mysqli = new mysqli($host, $user, $password, $db_name);
//prepare
$stmt = $mysqli->prepare("SELECT * FROM the_table WHERE field1= ? AND Field2= ?");
//Binding parameters. Types: s = string, i = integer, d = double, b = blob
$params= array("ss","string_1","string_2");
//now we need to add references
$tmp = array();
foreach($params as $key => $value) $tmp[$key] = &$params[$key];
// now us the new array
call_user_func_array(array($stmt, 'bind_param'), $tmp);
$stmt->execute();
/* Fetch result to array */
$res = $stmt->get_result();
while($row = $res->fetch_array(MYSQLI_ASSOC)) {
$a_data[]=$row;
}
print_r($a_data);
$stmt->close();