C# nullable types

In C#, a nullable type is a value type that can also have a value of null. A value type, such as an integer (int), double (double), or boolean (bool), is a type that represents a value rather than a reference to an object. By default, value types cannot be null.

Nullable types are useful when you need to represent situations where a value might be missing or unknown. For example, if you have a database field that can contain a number or no value at all, you can use a nullable integer (int?) to represent that field.

To create a nullable type in C#, you use the ? character after the data type. For example:

int? nullableInt = null;
double? nullableDouble = 3.14;
bool? nullableBool = false;

Here, nullableInt has no value (null), nullableDouble has a value of 3.14, and nullableBool has a value of false.

You can also use the Nullable<T> struct to create a nullable type. For example:

Nullable<int> nullableInt = null;
Nullable<double> nullableDouble = 3.14;
Nullable<bool> nullableBool = false;

To access the value of a nullable type, you can use the Value property or the null coalescing operator (??). For example:

int? nullableInt = 10;
int intValue = nullableInt.Value;        // intValue is 10

int? nullableInt2 = null;
int intValue2 = nullableInt2 ?? 0;       // intValue2 is 0

In the first example, intValue is assigned the value of nullableInt, which is 10. In the second example, intValue2 is assigned the value of nullableInt2, which is null, so the null coalescing operator assigns the value 0 to intValue2.

Note that you cannot use the Value property on a nullable type that has no value (null), as it will throw a InvalidOperationException.