Just for future reference, the count in PHP is used to detect the size of an array. PHP being more relaxed of a language, you can assign array blocks "as you go". I think they wanted to know how to get the counf of, say, variables starting with friends (such as friends[1] friends[2] etc). Just so you know in the mean time, you can use a wilcard such as $var(%friends[*], 0) that would tell you the number of variables matching the friends[<number>] pattern.
Just thought i would throw that in there.