Dynamic Calender Create

StringBuilder sb = new StringBuilder();
                sb.Append("<table style="border: 2px solid;width:100%;"><tr><th colspan="7" style="text-align: center;height:40px;">" + DateTime.Now.ToString("Y") + "</th></tr><tr><th style="text-align: center;">Su</th><th style="text-align: center;">Mo</th><th style="text-align: center;">Tu</th><th style="text-align: center;">We</th><th style="text-align: center;">Th</th><th style="text-align: center;">Fr</th><th style="text-align: center;">Sa</th></tr>");
                int year = DateTime.Now.Year;
                int month = DateTime.Now.Month;
                int totaldays = DateTime.DaysInMonth(year, month);

                DateTime firstDay = new DateTime(DateTime.Today.Year, DateTime.Today.Month, 1);
                DateTime lastDay = new DateTime(DateTime.Today.Year, DateTime.Today.Month, totaldays);

                int firstdate = (int)firstDay.DayOfWeek;
                int lastdate = (int)lastDay.DayOfWeek;

                DateTime PrelastDay = new DateTime(year, month, 1).AddDays(-1);
                int Preday = PrelastDay.Day;

                DateTime NextFirstDay = new DateTime(year, month, 1).AddMonths(1);
                int Nextday = NextFirstDay.Day;

                int counter = 0;

                for (int j = 0; j < firstdate; j++)
                {
                    if (counter == 0)
                    {
                        sb.Append("<tr>");
                    }
                    sb.Append("<td class="PrevAfterMonth">" + (Preday - firstdate + 1) + "</td>");
                    counter += 1;
                    Preday++;
                    if (counter == 7)
                    {
                        sb.Append("</tr>");
                        counter = 0;
                    }
                }

                for (int i = 1; i <= totaldays; i++)
                {
                    if (counter == 0)
                    {
                        sb.Append("<tr>");
                    }

                    counter += 1;

                    DateTime todate = Convert.ToDateTime(i + "/" + month + "/" + year);
                    sb.Append("<td class="CurrentMonth">" + i + "</td>");

                    if (counter == 7)
                    {
                        sb.Append("</tr>");
                        counter = 0;
                    }
                }

                if (lastdate == 0) lastdate += 6;
                else if (lastdate == 1) lastdate += 4;
                else if (lastdate == 2) lastdate += 2;
                else if (lastdate == 3) lastdate = 3;
                else if (lastdate == 4) lastdate -= 2;
                else if (lastdate == 5) lastdate -= 4;
                else if (lastdate == 6) lastdate += 1;

                for (int k = 0; k < lastdate; k++)
                {
                    if (counter == 0)
                    {
                        sb.Append("<tr>");
                    }
                    sb.Append("<td class="PrevAfterMonth">" + Nextday + "</td>");
                    counter += 1;
                    Nextday++;
                    if (counter == 7)
                    {
                        sb.Append("</tr>");
                        counter = 0;
                    }
                }
                sb.Append("<table>");
</table></table>