Capture the current value in a variable.

I have a radio button list and dropdown .when user select an option from radio button -
dropdown change dynamically.

I need to capture current value in a variable.
how can i do that

It is like asking this sort of question. "When there is a fire, there is a smoke. So how far would New York be from LA?"

You need to be specific about what you are asking. Do you want code for changing the drop down dynamically when an option is selected, then use Ajax/javascript.