How to check checkbox in smarty?

Question

PHP

I'm creating a checkbox in a template in a .tpl file
How can I check if the checkbox is pressed just below?

<input type="checkbox" name='is_ifnc' value='1' class=button >

I need to click on it and then I click on the "show" button. If the checkbox is clicked and I click "show", then a new column should be added, otherwise nothing is added?
I tried like this:

{if isset($is_ifnc)}<td>Новая колонка появись</td> {/if}