How convert Gregorian date to Persian date?

    DateTime date = new DateTime(2013, 10, 24);
    var calendar = new PersianCalendar();
    var persianDate = new DateTime(calendar.GetYear(date), calendar.GetMonth(date), calendar.GetDayOfMonth(date));
    var result = persianDate.ToString("yyyy MMM ddd", CultureInfo.GetCultureInfo("fa-Ir"));

You can use PersianDateTime:

PM> Install-Package PersianDateTime

The Reference: PersianDateTime

You can use string.Split() if you need customization.

Use the PersianCalendar:

string GregorianDate = "Thursday, October 24, 2013";
DateTime d = DateTime.Parse(GregorianDate);
PersianCalendar pc = new PersianCalendar();
Console.WriteLine(string.Format("{0}/{1}/{2}", pc.GetYear(d), pc.GetMonth(d), pc.GetDayOfMonth(d)));

Adding up to other answers, You can get the first one by using PersianDateTime:

var gregorianDate = "Thursday, October 24, 2013";
var date = DateTime.Parse(gregorianDate);
var persianDate = new PersianDateTime(date);
var result = persianDate.ToString("dddd d MMMM yyyy");