Error date_modify() expects parameter 1 to be DateTime : <p>Full code :</p>

<pre><code>$ngayhientai = date("d/m/Y");
        $ngaygiao = date_create($ngayhientai,timezone_open("Asia/Ho_Chi_Minh"));
        $ngaygiao = date_modify($ngayhientai,"+3 days");
        $ngaygiao = date_format($ngayhientai,"d/m/Y") ;

        echo $ngaygiao;
</code></pre>

<p>Error :</p>

<pre><code>Warning: date_modify() expects parameter 1 to be DateTime, string given in C:\xampp\htdocs\weblazada\dulieu.php on line 8

Warning: date_format() expects parameter 1 to be DateTimeInterface, string given in C:\xampp\htdocs\weblazada\dulieu.php on line 9
</code></pre>

<p>Help me!Thank you everybody</p>
