C# - Basic question: What is '?'? [duplicate]

Answer 1

The ? is a nullable value type.

You can use the ?? operator to mix it with value types:

const int DefaultValue = -1;

// get a result that may be an integer, or may be null
int? myval = GetOptionalIdFromDB();

// the value after ?? is used if myval is null
int nonNullable = myval ?? DefaultValue;

The nullable type can be compared to null, so the above is shorthand for:

if( myval != null ) {
    nonNullable = myval.Value;
} else {
    nonNullable = DefaultValue;
}

But I prefer ??