public void EnrolInstructorToCourse(int courseID, int instructorID) { // check if course exists ICourseRepository courseRepo = new CourseRepository(); if (!courseRepo.IsCourseExist(courseID)) { // course not exists throw new CourseNotFondException(courseID + " is not a registered course."); } courseRepo.EnrolInstructorToCourse(courseID, instructorID); }