private void dgvRegistro_CellEndEdit(object sender, DataGridViewCellEventArgs e)
 {
     try
     {
         pr.CuadroNotas(dgvRegistro, cbGrado, cbMateria, cbSeccion, rbt1, rbt2, rbt3, rbp35,
                        rbs35, rb30);
     }
     catch (Exception)
     {
         MessageBox.Show("Ingrese datos válidos", "ERROR", MessageBoxButtons.OK, MessageBoxIcon.Error);
         dgvRegistro.CurrentCell.Value = "0";
         pr.CuadroNotas(dgvRegistro, cbGrado, cbMateria, cbSeccion, rbt1, rbt2, rbt3, rbp35,
                        rbs35, rb30);
     }
 }