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);


        }
    }
}

.NET Calculate week number of a date

This post shows a way to calculate the number of weeks.

Remember that this calculation is culture-dependant

For example the GetWeekOfYear methods requires a criteria to determine 

how to determine the first week and which day to consider as FirstDayOfWeek for more info see here:

CalendarWeekRule.FirstDay

Supported by the .NET Compact Framework.

Indicates that the first week of the year starts on the first day of the year and ends before the following designated first day of the week. The value is 0.

CalendarWeekRule.FirstFourDayWeek

Indicates that the first week of the year is the first week with four or more days before the designated first day of the week. The value is 2.

CalendarWeekRule.FirstFullWeek

Indicates that the first week of the year begins on the first occurrence of the designated first day of the week on or after the first day of the year. The value is 1.

Sample Code

        Dim x As Date
        Dim currentCulture As System.Globalization.CultureInfo
        currentCulture = CultureInfo.CurrentCulture
        Dim weekNum = currentCulture.Calendar.GetWeekOfYear(x, CalendarWeekRule.FirstFourDayWeek, DayOfWeek.Monday)