Finding first day of calendar

Question

What i want to do is to create a simple calendar, and I want to find the first day of the first week of a specific month. My calendar is a Monday -> Sunday calendar and the following code works, but as you can see it's not that nice. Anyone have any better idea on how to get the first date in the calendar.

var now = new DateTime(Year, Month, 1);
now = now.AddDays(1-(int)now.DayOfWeek);
now = now.Day > 15 ? now : now.AddDays(-7);

The calendar will end up looking like this:

| <  |        Jan  2011       |  > |
------------------------------------
| Mo | Tu | We | Th | Fr | Sa | Su |
|[27]| 28 | 29 | 30 | 31 | 01 | 02 |
| 03 | 04 | 05 | 06 | 07 | 08 | 09 |
| .. | .. | .. | .. | .. | .. | .. |
| .. | .. | .. | .. | .. | .. | .. |
| 31 | 01 | 02 | 03 | 04 | 05 | 06 |

And in this "image" it's the [27] date that i'm trying to find.

Solution (Found i better/cleaner to loop then calculate):

    public DateTime FirstDay()
    {
        var date = new DateTime(Date.Year, Date.Month, 1);
        while (true)
        {
            if (date.DayOfWeek == DayOfWeek.Monday)
                return date;
            date = date.AddDays(-1);
        }
        return date;
    }

    public DateTime LastDay()
    {
        var date = new DateTime(Date.Year, Date.Month, 
                                DateTime.DaysInMonth(Date.Year, Date.Month));
        while (true)
        {
            if (date.DayOfWeek == DayOfWeek.Sunday)
                return date;
            date = date.AddDays(1);
        }
        return date;
    }

/BR Andreas

Answer 1

I would just do this. It is so easy to understand:

var firstDayOfMonth = new DateTime(year, month, 1);
DateTime startOfCalendar = 
    FirstDayOfWeekOnOrBefore(
        firstDayOfMonth,
        DayOfWeek.Monday
    );

public static DateTime FirstDayOfWeekOnOrBefore(
    DateTime date,
    DayOfWeek dayOfWeek
) {
    while(date.DayOfWeek != dayOfWeek) {
        date = date.AddDays(-1);
    }
    return date;
}

Additionally, if you want to change your calendar to start on something other than Monday, it's trivial now. A solution using modulo arithmetic would not be as maintainable.