A small, private university specializing in graduate programs needs to keep track of the list of students who (a) apply, (b) are accepted, and (c) actually enroll in the university. For security purposes the university also must send a report to the government with a list of foreign students who enroll but fail to register. Suggest a kind of code for this purpose, and give an example of its use in the university that demonstrates its appropriateness. What are its advantages?