Getting the value from Dropdown and pass it to URL address of Dynamic Dropdown as parameter

Question

I have a simple Dropdown ( control-30) with

'label1'...'labelN'

that has values

'val1'...'valN'

Selecting, let's say, label2 to pass the corresponding val2 to a dynamic dropdown with Requested URL http://example.com/demo?code=???? (e.g. {$control-30}, etc.) How can I do that or there is no way inside the contro-settings dialog box to do that but only inside the form as a code. Can you give an example? For example, a solution would be like : http://example.com/demo?code={$control-30}

Answer 1

The answer is simple : http://example.com/demo?code={../control-30}