string TaoMaDGMoi()
{
DocGiaDAO book = new DocGiaDAO();
string old = book.getMaxMaDG();
old = old.TrimStart('D');
old = old.TrimStart('G');
int newCode = int.Parse(old);
newCode += 1;
string code = "DG";
if (newCode < 10)
{
code = code + "00" + newCode;
}
else if (newCode < 100)
{
code = code + "0" + newCode;
}
else
{
code = code + newCode;
}
return(code);
}