If you are defining and setting the $nc variable within your script, and want to pass it along when the form is submitted, then pass it as a hidden variable.
print('<input type="hidden" name="nc" value="'.!empty($nc) ? $nc : ''.'">');
This will create a hidden variable named "nc". It will set the value to the value of $nc as long as nc is not empty. If it is empty, it will set the value to blank.
When referring to your variable after submission, unless your global variables are set on then you have to use something like $_POST['nc'] or $_REQUEST['nc']