Display values of current POST request on page

You can use filter_var or, more directly, filter_input to retrieve data from the REQUEST data.

$var_a = filter_input( INPUT_POST, 'var_a', FILTER_SANITIZE_STRING );

The above code will get var_a out of the $_POST data, and sanitize according to PHP’s FILTER_SANITIZE_STRING. You can read the PHP Manual on Types of filters for other data types.