Can't connect with mysql db getting error "Fatal error: Class 'mysql_connect' not found in.."

Can't connect with mysql db getting error "Fatal error: Class
'mysql_connect' not found in.."

I am learning the core php and write the below code for testing connection
with db getting "Fatal error: Class 'mysql_connect' not found in
C:\xampp\htdocs\demo\index.php on line 4" erro, code is below
<?php
$dbcon = new mysql_connect("localhost","root","");
mysql_select_db("demo", $dbcon);
$query = mysql_query("select name FROM test ");
echo mysql_num_row($query);
mysql_close($dbcon);
?>