title: Variable could't be recognized by server
body: <pre><code>&lt;pre&gt;
  $query = "select * from user WHERE username = '$username'";
                      $query_run = mysqli_query($con,$query);
  &lt;/pre&gt;
  </code></pre>
  
  <p>When I execute the program it show me this message. Undefined variable: con in </p>