private SqlConnection con;
private DataTable dt = new DataTable("Luu");
private SqlDataAdapter da = new SqlDataAdapter();

private void connect()
{
    //(local):tên sever   QuanLy: tên DB  Luu: tên table
    String cn = @"Data Source=(local);Initial Catalog=QuanLy;Integrated Security=True";
    try
    {
         con = new SqlConnection(cn);
         con.Open(); //Mở kết nối
    }
    catch (Exception ex)
    {
         MessageBox.Show("Không thể kết nối tới dữ liệu!", "Error", MessageBoxButtons.OK, MessageBoxIcon.Error);
    }
}

private void disconnect()
{
    con.Close(); //Đóng kết nối
    con.Dispose(); //Giải phóng tài nguyên
    con = null; //Hủy đối tượng
}

private void getdata()
{
     SqlCommand command = new SqlCommand(); //Khai báo 1 command
     command.Connection = con; //Kết nối
     command.CommandType = CommandType.Text; //Khai báo kiểu command
     command.CommandText = "Select * From Luu";

     da.SelectCommand = command;
     da.Fill(dt);
     dataGridViewX1.DataSource = dt;

        }

//lưu dữ liệu đã nhập từ các textBox vào DB
private void btnLuu_Click(object sender, EventArgs e)
{
    DataRow row = dt.NewRow();

    row["HọTên"] = txtHoten.Text;
    row["GiớiTính"] = txtGioi.Text;
    
    dt.Rows.Add(row);
    SqlCommand cmdInsert = new SqlCommand();
    cmdInsert.Connection = con;
    cmdInsert.CommandType = CommandType.Text;

    cmdInsert.CommandText = @"INSERT INTO DanhSach2 ( HọTên, GiớiTính)
                                           VALUES ( @HọTên, @GiớiTính) ";
    cmdInsert.Parameters.Add("@HọTên", SqlDbType.NVarChar, 50, "HọTên");
    cmdInsert.Parameters.Add("@GiớiTính", SqlDbType.NVarChar, 50, "GiớiTính");

    da.InsertCommand = cmdInsert;
    da.Update(dt);
    MessageBox.Show("Bạn đã thêm thành công!", "THÔNG BÁO", MessageBoxButtons.OK);
    Close();
    disconnect();
    Dispose();
}

Line 1: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'SqlConnection'
Line 2: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'DataTable'
Line 3: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'SqlDataAdapter'
Line 5: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'void'
Line 8: error: stray '@' in program
Line 20: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'void'
Line 27: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'void'
Line 41: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'void'
Line 53: error: stray '@' in program
Line 53: error: missing terminating " character
Line 54: error: stray '@' in program
Line 54: error: stray '\341' in program
Line 54: error: stray '\273' in program
Line 54: error: stray '\215' in program
Line 54: error: stray '\303' in program
Line 54: error: stray '\252' in program
Line 54: error: stray '@' in program
Line 54: error: stray '\341' in program
Line 54: error: stray '\273' in program
Line 54: error: stray '\233' in program
Line 54: error: stray '\303' in program
Line 54: error: stray '\255' in program
Line 54: error: missing terminating " character