public string Shamsi(string date)
{
int[] arrMonths ={ 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };
int[] arrStart ={ 21, 20, 21, 21, 22, 22, 23, 23, 23, 23, 22, 22 };
char[] sep ={ '/' };
string[] arrDate = date.Split(sep);
int year = Convert.ToInt32(arrDate[0]);
int month = Convert.ToInt32(arrDate[1]);
int day = Convert.ToInt32(arrDate[2]);

if (year % 4 == 0)
{
for (int i = 2; i < 12; i++)
arrStart[i]--;
arrMonths[1]++;
if (month == 1) arrStart[11]++;
}
else if (year % 4 == 1)
{
arrStart[0]--;
arrStart[1]--;
if (month == 1) arrStart[11]--;
}
year = month <= 3 ? year - 622 : year - 621;
if (month == 3 && day >= arrStart[2]) year++;
if (day < arrStart[month - 1])
{
int i = month == 1 ? 11 : month - 2;
day = day - arrStart[i] + arrMonths[i] + 1;
month -= 3;
}
else
{
day = day - arrStart[month - 1] + 1;
month -= 2;
}
if (month <= 0) month += 12;
return year + "/" + Convert.ToString(month).PadLeft(2,'0') + "/" +
Convert.ToString(day).PadLeft(2,'0');
}