string TaoMoiMaPhieu() { PhieuMuonDAO pm = new PhieuMuonDAO(); string old = pm.GetMaxMaPhieu(); old = old.TrimStart('P'); int newCode = int.Parse(old); newCode += 1; string code = "P"; if (newCode < 10) { code = code + "00" + newCode; } else if (newCode < 100) { code = code + "0" + newCode; } else { code = code + newCode; } return(code); }