How to show dropdown select box according to selection from the other one?

[eluser]term25[/eluser]
I have a select box where you can chose a country (USA, Canada, Mexico, Germany etc.) and the second one with cities.

I need to achieve that when you select a state e.g. USA from the first selectbox, then in the second selectbox shows cities like New York, Los Angeles etc.

How to achieve that in CodeIgniter?

Does CI have some function or something to do that?