verify a field

Hi,
Sorry if this question has been asked, is there a way to verify a field .e.g I got a field which asked: ‘Number of guest (which is a required field)’ if the user enter more than 1 then a other field appear and asking for their ‘name’

Cheers,
Sop

http://ww.wp.xz.cn/extend/plugins/visual-form-builder/