Create shortcode in wordpress

      [my_ad_code]
     
       // The shortcode function
function wpb_demo_shortcode_2() {

// Advertisement code pasted inside a variable
$string .= '<script async src="//pagead2.googlesyndication.com/pagead/js/adsbygoogle.js"></script>
<ins class="adsbygoogle"
     style="display:block; text-align:center;"
     data-ad-format="fluid"
     data-ad-layout="in-article"
     data-ad-client="ca-pub-0123456789101112"
     data-ad-slot="9876543210"></ins>
<script>
     (adsbygoogle = window.adsbygoogle || []).push({});
</script>';

// Ad code returned
return $string;

}
// Register shortcode
add_shortcode('my_ad_code', 'wpb_demo_shortcode_2');