Assign variable from a controller to tpl file

[beginner1]

Hi everyone, I have created a front-office controller in which I have set up a tpl file as template. I want to assign a variable such that it can be used in the tpl file through smarty. The variable should be assigned in the front-office controller. I have tried the following statements but they don't work.

 

$this->context->smarty->assign('my_var', $results);              // this works in the module.php file but not in the controller file

$smarty->assign('my_var', $length);