Variable type ending with ?

Question

What does ? mean:

public bool? Verbose { get; set; }

When applied to string?, there is an error:

Answer 1

bool? is a shorthand notation for Nullable. In general, the documentation states:

The syntax T? is shorthand for Nullable, where T is a value type. The two forms are interchangeable

Since string is not a value type (it's a reference type), you cannot use it as the generic parameter to Nullable.