private void delete__Click(object sender, EventArgs e)
        {
            int             curruentRow = dataGridView1.CurrentCell.RowIndex;
            DataGridViewRow selectedRow = dataGridView1.Rows[curruentRow];

            dataGridView1.Rows.Remove(dataGridView1.Rows[curruentRow]);
            Student.delete_student(curruentRow);
            //MessageBox.Show(curruentRow.ToString());
        }