Untitled

<?php
$server="localhost";
$username="root";
$password="admin007#";
$dbname="demo";

$con=new mysqli($server,$username,$password,$dbname);
if(!$con)
{
  die('error connecting to the database');
}


if(isset($_POST['login'])){
$a=mysqli_real_escape_string($con, $_POST['user']);
$b=mysqli_real_escape_string($con, $_POST['pass']);
$sql="SELECT * FROM login WHERE username='$a' AND password='$b'";
$result=mysqli_query($con, $sql);
$check=mysqli_num_rows($result);
if($check>0){
    echo "you are logged in";
}
else
{
    echo "Error";
}
}

?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>Untitled Document</title>
</head>

<body>
<tr>
<td>Username:</td>
<td><input type="text" name="user" value=""/></td>
</tr><br /><br />
<tr>
Password:
<td><input type="password" name="pass" value=""/></td>
</tr><br />
<tr align="center"><td colspan="2"><input type="submit" name="login" value="Log In"/></td></tr>
</body>
</html>