private void CourseRemove_Click(object sender, EventArgs e)//删除按钮功能
        {
            var rows = CourseList.SelectedRows;

            if (rows.Count > 0)
            {
                DialogResult result = MessageBox.Show("确定要删除吗?", "提示", MessageBoxButtons.OKCancel);
                if (result == DialogResult.Cancel)
                {
                    return;
                }
                string    cno       = rows[0].Cells[0].Value.ToString();
                CourseBLL courseBLL = new CourseBLL();
                if (courseBLL.Remove(cno))
                {
                    MessageBox.Show("删除成功");
                    LoadCourseList();
                }
                else
                {
                    MessageBox.Show("删除失败");
                }
            }
            else
            {
                MessageBox.Show("请选择要删除的行");
            }
        }