public string PhatSinhMa()
{
int so = dg_DAO.DemDocGia(); // 6
string Ma = "DG";
int idem = 0;
foreach (char x in so.ToString()) // co 1 ki tu
{
idem++; // idem = 1
}
for (int i = 0; i < 8 - idem; i++) // 7 so 0
{
Ma += "0";
}
Ma += so.ToString(); // 6
return(Ma);
}