Hi
Try like this..
DateTime v_todaydt = DateTime.Today;
var v_DespatchDate = v_todaydt.AddDays(7).Date.ToString("yyyy/MM/dd");
DateTime dateTime = DateTime.ParseExact(v_DespatchDate, "yyyy/MM/dd", System.Globalization.CultureInfo.InvariantCulture);
var dayname = (dateTime.ToString("dddd"));
for casting use :
DateTime.ParseExact
for getting day name use :
.ToString("dddd")