Convert Date from Persian to Gregorian

It’s pretty simple actually:

// I'm assuming that 1391 is the year, 4 is the month and 7 is the day
DateTime dt = new DateTime(1391, 4, 7, persianCalendar);
// Now use DateTime, which is always in the Gregorian calendar

When you call the DateTime constructor and pass in a Calendar, it converts it for you – so dt.Year would be 2012 in this case. If you want to go the other way, you need to construct the appropriate DateTime then use Calendar.GetYear(DateTime) etc.

Short but complete program:

using System;
using System.Globalization;

class Test
{
    static void Main()
    {
        PersianCalendar pc = new PersianCalendar();
        DateTime dt = new DateTime(1391, 4, 7, pc);
        Console.WriteLine(dt.ToString(CultureInfo.InvariantCulture));
    }
}

That prints 06/27/2012 00:00:00.