test checkbox value

using the gform_after_submission action, I'm retrieving the values of the $entry variable.
I could get the value from a textbox and a radio group, but how do I get it from a checkbox?
radio group:
if($entry[1] == 'choice 1')
// do something
elseif($entry[1] == 'choice 2')
//do something else

this works with radio buttons

thanks, I figured it out:
using $entry[3.1] doesn't seem to work, but when wrapping it in quotes, it does
$entry['3.1'] = '1'
and I set the checkbosx to have a value in the form settings