You may want to check out this zip file that contains some VENUS challenges on arrays and barcoding. It includes a word document that reads like a set of basic user requirements and with each exercise, it adds more feature requests so you can iteratively build a more complex method. See below for an excerpt of Exercise 1:
The zip file contains completed examples of each exercise so you can compare.
Part of the point of the exercise is to also anticipate what may be needed to make a more usuable and supportable program. Your internal customer is not necessarily going to ask you to add tip counters, check for volume/tip compatability, trace info to the log file, etc.