Multiple values per variable

I am working on some logic where users are categorized based on the results from a few questions. So far everything is working properly, but I would like to be able to assign multiple categories to each user. Any ideas on how to accomplish this? I am assuming that an array would be in order, but not to sure on the syntax, or how to "explode" the array (eg. User is a member of $cat[1], $cat[2], $cat[3], etc.