private void btnDelete_Click(object sender, EventArgs e)
        {
            if (!cu.is_dataGridView_colored(dataGridViewMorimProject))
            {
                MessageBox.Show("Nothing is picked on table!");
                return;
            }
            string    a         = cu.GetID(dataGridViewMorimProject);
            Lessons   les       = new Lessons();
            DataTable lessonsID = les.GetLessonsTeachersStudentId();

            foreach (DataRow dr in lessonsID.Rows)
            {
                if (dr["teacher_id"].ToString() == a && cu.is_date_in_future(dr["due_date"].ToString()))
                {
                    MessageBox.Show(dr["due_date"].ToString());
                    MessageBox.Show("Cannot delete teachers with scheduled lessons!");
                    return;
                }
            }
            MorimProject mkk = new MorimProject();

            mkk.DeleteButton(a);
            cu.charge_data_grid_view(mkk.GetMorim(), dataGridViewMorimProject);
            dataGridViewMorimProject.ClearSelection();
        }
        private void btnDelete_Click(object sender, EventArgs e)
        {
            if (!cu.is_dataGridView_colored(dataGridViewStudents))
            {
                MessageBox.Show("Nothing is picked on table!");
                return;
            }
            string    a         = cu.GetID(dataGridViewStudents);
            Lessons   les       = new Lessons();
            string    field     = "student_id";
            DataTable lessonsID = les.GetLessonsTeachersStudentId();

            foreach (DataRow dr in lessonsID.Rows)
            {
                if (dr[field].ToString() == a && cu.is_date_in_future(dr["due_date"].ToString()))
                {
                    MessageBox.Show("Cannot delete student with scheduled lessons!");
                    return;
                }
            }
            Student mkk = new Student();

            mkk.Delete(a);
            tan();
            dataGridViewStudents.ClearSelection();
        }