private void Form1_Load(object sender, EventArgs e)
    {
        using (StreamReader sr = new StreamReader("course.txt"))
        {
            string cNumber;
            while ((cNumber = sr.ReadLine()) != null)
            {
                string cTitle = sr.ReadLine();
                **int numRegistered = int.Parse(sr.ReadLine());**
                // create the course
                Course c = new Course(cNumber, cTitle, numRegistered);
                allCourses.Add(c);
                courseNumComboBox.Items.Add(c.CNumber);
            }