//删除教师
        private void button11_Click(object sender, EventArgs e)
        {
            if (MessageBox.Show("确定要删除吗?", "询问", MessageBoxButtons.YesNo) == DialogResult.Yes)
            {

                bool isDeleteOk = true;
                TeacherBusiness teaBusiness = new TeacherBusiness();
                DataGridViewSelectedRowCollection toBeDeletedRowsCollection = this.dataGridView2.SelectedRows;
                DataGridViewRow[] tobedeletedrows = new DataGridViewRow[toBeDeletedRowsCollection.Count];
                toBeDeletedRowsCollection.CopyTo(tobedeletedrows, 0);
                foreach (DataGridViewRow temp in tobedeletedrows)
                {
                    if (teaBusiness.deleteTeacher(int.Parse(temp.Cells["tid"].Value.ToString())) == 0)
                        isDeleteOk = false;
                }
                if (isDeleteOk)
                {
                    MessageBox.Show("删除成功!");
                }
                else
                {
                    MessageBox.Show("删除出现错误,请刷新列表后重试!");
                }
            }
        }