8.6 Nullable Types

Let’s go through nullable types in C# — a way to allow value types to represent null.

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📌 1. What Are Nullable Types?

• Normally, value types like int, double, bool cannot be null.

• Nullable types allow these types to also have a null value, useful for optional data or database mapping.

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📌 2. Syntax

There are two ways to declare nullable types:

int? nullableInt = null;     // Using ?
Nullable<int> anotherInt = null;  // Using Nullable<T>

• int? is shorthand for Nullable<int>

• Works with all value types (int, double, bool, DateTime, etc.)

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📌 3. Checking for Value

Use .HasValue or compare to null:

int? age = null;
 
if (age.HasValue)
    Console.WriteLine("Age: " + age.Value);
else
    Console.WriteLine("Age is not provided"); // Output

• .Value gives the actual value

• Accessing .Value when null throws InvalidOperationException

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📌 4. Using Null-Coalescing Operator (??)

• Provides a default value if the nullable is null

int? age = null;
int displayAge = age ?? 18;  // If age is null, use 18
Console.WriteLine(displayAge); // 18

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📌 5. Nullable Boolean Example

bool? isActive = null;
 
if (isActive == true)
    Console.WriteLine("Active");
else if (isActive == false)
    Console.WriteLine("Inactive");
else
    Console.WriteLine("Status unknown"); // Status unknown

• Nullable booleans allow three states: true, false, null

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📌 6. Nullable in Expressions

int? a = 5;
int? b = null;
 
int? sum = a + b; // sum is null because b is null

• Arithmetic operations propagate null if any operand is null

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📌 7. Summary Table

Feature	Description
Syntax	int? x or Nullable<int> x
Checking for value	x.HasValue or x != null
Accessing value	x.Value
Default value	x ?? defaultValue
Use Case	Optional data, database fields, three-state logic (e.g., nullable bool)

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✅ Tip:

• Use nullable types for optional fields or database-mapped value types

• Combine with null-coalescing (??) and null-conditional (?.) operators for clean code