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nullable types
Under many circumstances a property or variable may be a value type which can be null. Previously defining a value type precluded the ability to assign null to it. For example, int b - b can not be null. However, the real world is different. With nullable types, you can permit a value type to be null. There are two way to indicate the nullable type. For example with int -
int ?
Nullable <int>
The ? marks that the int is nullable. Nullable <int> is an example of generics, an instance of the System.Nullable<T>. int? is a short hand which actually creates the Nullable