using System;

    using System.Globalization;

​

public class Program

{

    public static void Main()

    {

        int year = 2019;

        int weekOfYear = 33;

        DateTime jan1 = new DateTime(year, 1, 1);

​

        int daysOffset = (int)CultureInfo.CurrentCulture.DateTimeFormat.FirstDayOfWeek - (int)jan1.DayOfWeek;

        Console.WriteLine("daysOffset = " + daysOffset) ;

        DateTime firstMonday = jan1.AddDays(daysOffset);

        Console.WriteLine("firstMonday = " + firstMonday) ;

        /* why need below ? 1/1 should must first week ?  I think directly weekOfYear -= 1; is ok ? */

        int firstWeek = CultureInfo.CurrentCulture.Calendar.GetWeekOfYear(jan1, CultureInfo.CurrentCulture.DateTimeFormat.CalendarWeekRule, CultureInfo.CurrentCulture.DateTimeFormat.FirstDayOfWeek);

        Console.WriteLine("firstWeek = " + firstWeek) ;

        if (firstWeek <= 1)

        {

            weekOfYear -= 1;

        }

        var tempDate = firstMonday.AddDays(weekOfYear * 7);

        Console.WriteLine("tempDate = " + tempDate) ;

        if (tempDate < DateTime.Parse(("01/01/" + year.ToString())))

        {

            tempDate = DateTime.Parse(("01/01/" + year.ToString()));

        }

        Console.WriteLine("calculated date = " + tempDate.ToString("dd/MM/yyyy")) ;

        if (tempDate > DateTime.Now)

        {

            tempDate = tempDate.AddYears(-10);

        }

        Console.WriteLine("finial date = " + tempDate.ToString("dd/MM/yyyy")) ;

        /*

         if (tempDate.Year < DateTime.Now.Year)

         {

             var temp = DateTime.Parse("01/01/" + tempDate.Year);

             Console.WriteLine("if calculated date < current year = " + temp.ToString("dd/MM/yyyy")) ;

         }

         if (tempDate.Year > DateTime.Now.Year)

         {

            var temp = tempDate.AddYears(-10);

            Console.WriteLine("if calculated date > current year = " + temp.ToString("dd/MM/yyyy")) ;

         }

         */

    }

}