public string PhatSinhMaSach()
{
int so = sach_DAO.DemSoLuongSach();
string Ma = "Sa";
int dem = 0;
foreach (char x in so.ToString())
{
dem++;
}
for (int i = 0; i < 8 - dem; i++)
{
Ma += "0";
}
Ma += so.ToString();
return Ma;
}