Question

I want to populate the weeks in a dropdown list when selecting month like
when I select

January 

Then it will show only the weeks which starts from monday like

1st week:
Monday(02/01/2012)
2nd week:
Monday(09/01/2012)
3rd week:
Monday(16/01/2012)
4th week:
Monday(23/01/2012)
5th week:
Monday(30/01/2012)

Answer 1

So it sounds like you need to find the first Monday in the week, then just keep adding one week until you’re not in the same month any more:

using System;
using System.Collections.Generic;

class Test
{
    static void Main(string[] args)
    {
        foreach (DateTime date in GetMondays(2012, 1))
        {
            Console.WriteLine(date);
        }
    }

    static IEnumerable<DateTime> GetMondays(int year, int month)
    {
        DateTime startOfMonth = new DateTime(year, month, 1);

        // Get to the first Monday
        int daysToMonday = DayOfWeek.Monday - startOfMonth.DayOfWeek;

        // Now make sure it's non-negative...
        int daysToNextMonday = (daysToMonday + 7) % 7;

        // Add it to the start of the month to get to the first Monday
        DateTime firstMonday = startOfMonth.AddDays(daysToNextMonday);

        // Now yield and iterate until we're done
        for (DateTime date = firstMonday;
             date.Month == month;
             date = date.AddDays(7))
        {
            yield return date;
        }
    }
}

(You could add the dates to a list and return that instead if you wanted… it doesn’t make much difference really.)