private void PreferredFilter_TextChanged(object sender, EventArgs e)
        {
            preferred_lecturers.DefaultView.RowFilter
                = string.Format("Name LIKE '%{0}%'", PreferredFilter.Text);
            for (int i = 0; i < PreferredLecturersCheckedListBox.Items.Count; ++i)
            {
                DataRowView row_view =
                    (DataRowView)PreferredLecturersCheckedListBox.Items[i];

                int id = Convert.ToInt32(row_view.Row.ItemArray[0]);
                if (preferred_lecturers_id.Contains(id))
                {
                    PreferredLecturersCheckedListBox.SetItemChecked(i, true);
                }
            }
        }
        private void ResetEverything()
        {
            PreferredFilter.Text = "";
            preferred_lecturers_id.Clear();
            foreach (int i in PreferredLecturersCheckedListBox.CheckedIndices)
            {
                PreferredLecturersCheckedListBox.SetItemChecked(i, false);
            }
            if (PreferredLecturersCheckedListBox.Items.Count > 0)
            {
                PreferredLecturersCheckedListBox.SelectedIndex = 0;
            }

            DeniedFilter.Text = "";
            if (DeniedLecturersCheckedListBox.Items.Count > 0)
            {
                DeniedLecturersCheckedListBox.SelectedIndex = 0;
            }
            denied_lecturers_id.Clear();
            foreach (int i in DeniedLecturersCheckedListBox.CheckedIndices)
            {
                DeniedLecturersCheckedListBox.SetItemChecked(i, false);
            }
        }