C#- Using Nullable Types

Nullable types can represent all the values of an underlying type, and an additional null value. Nullable types are declared in one of two ways:

System.Nullable variable

-or-C

T? variable

T is the underlying type of the nullable type. T can be any value type including struct; it cannot be a reference type.

For an example of when you might use a nullable type, consider how an ordinary Boolean variable can have two values: true and false. There is no value that signifies "undefined". In many programming applications, most notably database interactions, variables can exist in an undefined state. For example, a field in a database may contain the values true or false, but it may also contain no value at all. Similarly, reference types can be set to null to indicate that they are not initialized.

This disparity can create extra programming work, with additional variables used to store state information, the use of special values, and so on. The nullable type modifier enables C# to create value-type variables that indicate an undefined value.

Examples of Nullable Types

Any value type may be used as the basis for a nullable type. For example:

C#

int? i = 10;
double? d1 = 3.14;
bool? flag = null;
char? letter = 'a';
int?[] arr = new int?[10];