private void AddToolStripMenuItem_Click(object sender, EventArgs e)
        {
            AddStudent add = new AddStudent();

            add.ShowDialog();
            Student S1 = new Student();

            S1 = add.S;
            if (S1.StudentID == default(int))
            {
                return;
            }
            if (Business.checkStudentInDB(S1.StudentID))
            {
                MessageBox.Show("This student already existed!");
                return;
            }
            Report.addStudentToDB(S1);
        }
        private void 학생추가ToolStripMenuItem_Click(object sender, EventArgs e)
        {
            AddStudent AS = new AddStudent();

            AS.ShowDialog();
        }