PHP Authentication Database Password problem

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I am a PHP beginner, wrote a database to verify the user's simple code, regardless of the lost or wrong account password can not be verified. Seek expert guidance

Reply to discussion (solution)

$res = Mysqli_query ($conn, $sql);
if ($row = Mysql_fetch_assoc ($res)) {

MySQL and mysqli are parallel two extensions and cannot be mixed!

$res = Mysqli_query ($conn, $sql);
if ($row = Mysql_fetch_assoc ($res)) {

MySQL and mysqli are parallel two extensions and cannot be mixed!

What should I write to solve the problem

$res = Mysqli_query ($conn, $sql);
if ($row = Mysql_fetch_assoc ($res)) {

MySQL and mysqli are parallel two extensions and cannot be mixed!

Changed to if ($row =mysqli_fetch_assoc ($res)) solved the problem, thanks to the great God

header ("content-type:text/html;    Charset=utf-8 "), class cls_mysqli{private $db _host=" localhost ";     Private $db _user= "root";    Private $db _password= "root";    Private $db _name= "test";    protected $sql;        Public $password;      function __construct ($id, $password) {$this->password = $password;    $this->sql = "Select password from admin where id = $id";        } function Checkpassword () {Global $link; $link = Mysqli_connect ($this->db_host, $this->db_user, $this->db_password, $this->db_name) or Die ("Database error: " .        Mysqli_connect_error ());        $res = Mysqli_query ($link, $this->sql);               if ($row _val = Mysqli_fetch_row ($res)) {if ($this->password = = $row _val[0]) {return true;              }else{return false;  }}}} $query = new Cls_mysqli (1, ' 123 ');p rint $query->checkpassword (); Mysqli_close ($link); 

@xuzuning
If structure executes a return, this mysqli resource how to release is reasonable.

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