Welcome to today's lesson! We'll be exploring a practical application of C++ sets by managing student enrollments for various courses. Imagine you're running an online course platform and need to handle enrollments, checks, and listings of students in different courses. std::unordered_set would be perfect for this kind of problem since it does not allow duplicates, ensuring that a student can't enroll in the same course more than once!

By the end of this session, you'll be well-versed in using sets for such tasks. Let’s dive in!

Here are the methods we need to implement in our enrollment system:

• void enroll(const std::string& student, const std::string& course);: This method adds a student to a course. If the student is already enrolled, it does nothing.
• bool unenroll(const std::string& student, const std::string& course);: This method removes a student from a course. It returns true if the student was enrolled and has now been removed. Otherwise, it returns false. If after unenrolling the student, the course becomes empty (no one is enrolled there), remove the course as well.
• bool is_enrolled(const std::string& student, const std::string& course);: This method checks if a student is enrolled in a course. It returns true if the student is enrolled and otherwise.