public void EnrollInCourse(Course course)
{
if (this.EnrolledCourses.ContainsKey(course.GetName()))
{
throw new DuplicateEntryInStructureException(this.UserName, course.GetName());
}
this.enrolledCourses.Add(course.GetName(), course);
}
public int CompareTo(Course other) => string.Compare(this.Name, other.GetName(), StringComparison.Ordinal);