//Chọn thêm sách
 private void btnThemSach_Click(object sender, EventArgs e)
 {
     frmThemSach form = new frmThemSach(this);
     form.ShowDialog(this);
 }
        //Chọn thêm sách
        private void btnThemSach_Click(object sender, EventArgs e)
        {
            frmThemSach form = new frmThemSach(this);

            form.ShowDialog(this);
        }