DateTime

ToShortDateString

Converts the value of the current DateTime? object to its equivalent short date string representation. If value is null then returns specified defaultValue.

DateTime? dateTime = null;
var result = dateTime.ToShortDateString("------"); // "------"

dateTime = new DateTime(2008, 09, 25, 11, 35, 52);
result = dateTime.ToShortDateString("------"); // "09/25/2008"

Same works for long DateTime representation - ToLongDateString()

ToString

Converts the value of the current DateTime? object to its equivalent string representation using the specified format and the formatting conventions of the current culture. If value is null then returns specified defaultValue

DateTime? dateTime = null;
var result = dateTime.ToString("------"); // "------"

dateTime = new DateTime(2008, 09, 25, 11, 35, 52);
result = dateTime.ToString("dd-MM-yyyy hh:mm:ss", "------"); // "25-09-2008 11:35:52"