C#: get date time given current date and day of week

        /// <summary>
        /// Returns the daytime of the day of the week that the specified date is in. 
        /// </summary>
        public static DateTime GetDayOfWeek(DateTime dayInWeek, DayOfWeek dayOfWeek)
        {            
            DateTime lastDayInWeek = dayInWeek.Date;
            int increment = 1;
            if (dayOfWeek < dayInWeek.DayOfWeek) {
                increment = -1;
            }

            while (lastDayInWeek.DayOfWeek != dayOfWeek)
            {
                lastDayInWeek = lastDayInWeek.AddDays(increment);                                
            }                
            return lastDayInWeek;
        }

implementation samples:

get the first day of the week:
DayOfWeek dayOfWeekPriority = DayOfWeek.Monday;
DateTime iniDatePriority = DateTime.Now;
DateTime endDatePriority =GetDayOfWeek(iniDatePriority, dayOfWeekPriority).AddDays(1);

get the last day of the week:
DayOfWeek dayOfWeekPriority = DayOfWeek.Friday;
DateTime iniDatePriority = DateTime.Now;
DateTime endDatePriority = DashboardManager.GetDayOfWeek(iniDatePriority, dayOfWeekPriority).AddDays(1);

Resource:
http://joelabrahamsson.com/getting-the-first-day-in-a-week-with-c/