Get date of first Monday of the week? [duplicate]

This is what i use (probably not internationalised):

DateTime input = //...
int delta = DayOfWeek.Monday - input.DayOfWeek;
DateTime monday = input.AddDays(delta);

The Pondium answer can search Forward in some case. If you want only Backward search I think it should be:

DateTime input = //...
int delta = DayOfWeek.Monday - input.DayOfWeek;
if(delta > 0)
    delta -= 7;
DateTime monday = input.AddDays(delta);

Something like this would work

DateTime dt = DateTime.Now;
while(dt.DayOfWeek != DayOfWeek.Monday) dt = dt.AddDays(-1); 

I'm sure there is a nicer way tho :)

public static class DateTimeExtension
{
    public static DateTime GetFirstDayOfWeek(this DateTime date)
    {
        var firstDayOfWeek = CultureInfo.CurrentCulture.DateTimeFormat.FirstDayOfWeek;

        while (date.DayOfWeek != firstDayOfWeek)
        {
            date = date.AddDays(-1);
        }

        return date;
    }
}

International here. I think as extension it can be more useful.