Construct a new student object. The client must provide a student number when creating a student. The student's name may optionally be specified at the time the object is created. Set the student's name to a given string. Enrol the student in a new subject.
Input is an integer representing a subject code number.
The subject code is stored in the list of subjects, if there is room for it. A student can't be studying the same subject more than once. Output from this method is a boolean flag indicating whether the enrolment was successful or not. Withdraw the student from a subject. Input is a subject code number.