Get the Week Number in C#

Here is some examples of how to determine the WeekNumber of a given Date

using System;
using System.Collections.Generic;
using System.Text;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {

        object index = DateTime.Now;
        int res = 0;
        //0    First day of year
        res = System.Globalization.CultureInfo.CurrentCulture.Calendar.GetWeekOfYear(
        Convert.ToDateTime(index), System.Globalization.CalendarWeekRule.FirstDay, System.Globalization.DateTimeFormatInfo.CurrentInfo.FirstDayOfWeek);

        //1    (Default) First four day week from Sunday
        res = System.Globalization.CultureInfo.CurrentCulture.Calendar.GetWeekOfYear(
        Convert.ToDateTime(index), System.Globalization.CalendarWeekRule.FirstFourDayWeek, DayOfWeek.Sunday);

        //2    First four day week from StartOfWeek
        res = System.Globalization.CultureInfo.CurrentCulture.Calendar.GetWeekOfYear(
                Convert.ToDateTime(index), System.Globalization.CalendarWeekRule.FirstFourDayWeek, System.Globalization.DateTimeFormatInfo.CurrentInfo.FirstDayOfWeek);

        //3    First full week from Sunday
        res = System.Globalization.CultureInfo.CurrentCulture.Calendar.GetWeekOfYear(
                Convert.ToDateTime(index), System.Globalization.CalendarWeekRule.FirstFullWeek, DayOfWeek.Sunday);
        
        //4    First full week from StartOfWeek
        res = System.Globalization.CultureInfo.CurrentCulture.Calendar.GetWeekOfYear(
                Convert.ToDateTime(index), System.Globalization.CalendarWeekRule.FirstFullWeek, System.Globalization.DateTimeFormatInfo.CurrentInfo.FirstDayOfWeek);


        }
    }
}