asp .net DropDownList下拉选择指定项

int i = 0;
                foreach (ListItem listItem in dd.Items)
                {
                    int itemCourseId = Convert.ToInt32(listItem.Value);
                    if (itemCourseId == courseId)
                    {
                        dd.SelectedIndex = i;
                        break;
                    }
                    i++;
                }