public string GetMaHoaDonNext(int congThem = 0)
{
string lastNumString = dal_hoaDon.GetMaHoaDonLast();
string lastNumStringRemove = lastNumString.Remove(0, 2); //Lay phan so ra
int lastNum = Int32.Parse(lastNumStringRemove);
int nextNum = lastNum + 1 + congThem;
string nextNumString = nextNum.ToString();
while (nextNumString.Length < 8)// gom 8 so
{
nextNumString = "0" + nextNumString;
}
return("HD" + nextNumString);
}