Nullable Types in C#

What are Nullable Types?

In C#, all value types (such as int, float, bool) must have a value. However, there are scenarios where a value type needs to represent "no value" or null, especially when dealing with databases or optional values. This is where nullable types come in. A nullable type can represent its normal value range plus null.

To declare a nullable type, use the ? symbol after the type. For example:

int? nullableInt = null;
        

Working with Nullable Types

You can check whether a nullable type has a value using the .HasValue property and retrieve the value using .Value. Additionally, the null-coalescing operator (??) allows you to assign a default value if the nullable type is null.

Example: Checking Nullable Types and Using Null-Coalescing Operator

int? nullableInt = null;

if (nullableInt.HasValue)
{
    Console.WriteLine("Value: " + nullableInt.Value);
}
else
{
    Console.WriteLine("No value");
}

int defaultValue = nullableInt ?? 10;  // if nullableInt is null, use 10
Console.WriteLine(defaultValue);
        

In this example, nullableInt is checked for a value using .HasValue, and the null-coalescing operator provides a default value if nullableInt is null.

Nullable Types in Action

Nullable types are particularly useful in scenarios where you interact with external data sources (e.g., databases) that might contain null values. For example, consider a situation where you fetch an integer value from a database, and the value might be null.

Example: Nullable Type in Database Interaction

int? fetchedAge = GetAgeFromDatabase();  // might return null

int age = fetchedAge ?? -1;  // Use -1 as default if age is null
Console.WriteLine(age);
        

In this example, the method GetAgeFromDatabase might return null if no age is available. The null-coalescing operator ensures that if fetchedAge is null, -1 is assigned to age.

Key Points to Remember

• A nullable type is declared using ? (e.g., int?, bool?).
• You can check if a nullable type has a value using .HasValue.
• Use the null-coalescing operator (??) to provide a default value if the nullable type is null.
• Nullable types are useful when dealing with optional values or values that might be null (e.g., database fields).