Convert.ToDateTime(string)

DateTimeFormatInfo dtFormat = new System.GlobalizationDateTimeFormatInfo();
dtFormat.ShortDatePattern = "yyyy/MM/dd";
DateTime  dt = Convert.ToDateTime("2014/10/10", dtFormat);

string dateString = "20141010";
DateTime dt = DateTime.ParseExact(dateString, "yyyyMMdd", System.Globalization.CultureInfo.CurrentCulture);