C# Nullable Types

In C#, Nullable types are used to represent a value type (like int, float, bool, etc.) that can also have a value of null.

Value types cannot normally be assigned a value of null because they have a default value (e.g., 0 for numeric types, false for bool, etc.), and null is reserved for reference types.

Nullable types allow you to assign null to a value type, indicating the absence of a value. The nullable version of a value type is created by appending a ? to the value type declaration.

Here are the examples of changing non-nullable types into nullable types.

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

Here, int?, bool?, and double? are nullable versions of int, bool, and double, respectively. You can also use the Nullable<T> structure to create nullable types.

Nullable<int> nullableInt = null;

To check if a nullable type has a value or is null, you can use the HasValue property or the null-conditional operator (?.).

To access the underlying value, you can use the Value property (but it's safer to use HasValue or null-conditional operator to avoid InvalidOperationException if the nullable type is null):

if (nullableInt.HasValue)
{
    int value = nullableInt.Value;
    // Do something with the value
}

or using the null-conditional operator.

int? nullableInt = SomeMethodThatMayReturnNull();
int value = nullableInt?.Value ?? defaultValue;

Nullable types are useful in scenarios where you want to represent the absence of a value for a value type, such as when working with databases where a column allows null values or when dealing with optional parameters.

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