Convert String to DateTime or DateTime to String (C#)

String to DateTime

String MyString  = "1999-09-01 21:34 PM";
DateTime MyDateTime = new DateTime();
MyDateTime =
DateTime.ParseExact(MyString, "yyyy-MM-dd HH:mm tt",null);
or
DateTime.ParseExact("12-Dec-2006", "dd-MMM-yyyy", DateTimeFormatInfo.InvariantInfo);

DateTime to String

MyDateTime = new DateTime(1999, 09, 01, 21, 34, 00);
String MyString;
MyString = MyDateTime.ToString("yyyy-MM-dd HH:mm tt");