static void Main(string[] args)
        {
            try {
                Student s1 = new Student("X00100551", "Mark Lordan", Sex.Male);
                Student s2 = new Student("X00101899", "Robert Kenny", Sex.Male);
                StudentClass R1 = new StudentClass("Mask", "Gary Clynch");
                R1.addStudent(s1);
                R1.addStudent(s2);

                Student mark = R1["X00100551"];
                Console.WriteLine("Name: " + mark.Name + "\nStudent Number: " + mark.Uid);
                Student robbie = R1[1];
                Console.WriteLine("Name: " + robbie.Name + "\nStudent Number: " + robbie.Uid);

                foreach(Student s in R1)
                {
                    Console.WriteLine(s.ToString());
                }
                Student missing = R1[-1];

            }
            catch(ArgumentException ae)
            {
                Console.WriteLine(ae.Message);
            }
            Console.ReadLine();
        }
        public bool addStudent(Student aStudent)
        {
            bool result = false;
            if (studentList == null)
            {
                result = true;
                studentList.Add(aStudent);
            }
            else
            {
                if ((studentList.Count(s => s.Uid == aStudent.Uid)) == 1)
                {
                        result = false;
                        throw new ArgumentException("This student ID already exists");

                    }
                    else
                    {
                        result = true;
                        studentList.Add(aStudent);
                    }

            }
            return result;
        }