What does one question mark following a variable declaration mean? [duplicate]

Answer 1

? makes a value type (int, bool, DateTime, or any other struct or enum) nullable via the System.Nullable type. DateTime? means that the variable is a System.Nullable. You can assign a DateTime or the value null to that variable. To check if the variable has a value, use the HasValue property and to get the actual value, use the Value property.