📦 C# Nullables – Use Nullable Types for Optional Values

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🧲 Introduction – Why Use Nullable Types in C#?

In C#, value types like int, bool, and DateTime normally cannot hold a null value. But in many real-world applications, you might need a way to represent “no value” or “unknown.” This is where nullable types come in. They enable value types to store null, making them more flexible for data processing and user input.

🎯 In this guide, you’ll learn:

• What nullable types are and how to declare them
• How to check for null values safely
• The role of the ?? and ?. operators
• Real-world examples and best practices

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🔍 Core Concept – What Are Nullables in C#?

A nullable type is a value type that can also hold a null value. C# provides this feature using the ? syntax.

🔹 Syntax:

int? age = null;
bool? isMember = true;

✅ Nullable types wrap a value type and allow null as a valid state.

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💻 Code Example – Nullable Basics

using System;

class NullableDemo
{
    static void Main()
    {
        int? score = null;

        if (score.HasValue)
            Console.WriteLine($"Score: {score.Value}");
        else
            Console.WriteLine("Score is not set.");
    }
}

📤 Output:

Score is not set.

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🔄 Null Coalescing Operator (??)

The ?? operator provides a default value if a nullable type is null.

int? age = null;
int finalAge = age ?? 18;  // If null, use 18
Console.WriteLine(finalAge);  // Output: 18

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🔍 Nullable with Ternary & Null-Conditional Operator

🔹 Null-Conditional ?.:

string? name = null;
Console.WriteLine(name?.Length);  // Output: nothing (null-safe)

🔹 Ternary Check:

bool? passed = null;
Console.WriteLine(passed == true ? "Passed" : "Failed or not set");

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⚙️ Use Cases – Where to Use Nullables

Use Case	Example
Optional user input	int? age = null;
Database null values	decimal? price = db.GetValue();
Conditional flags	bool? isActive = GetStatus();
Config defaults or overrides	int? timeout = null;

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💡 Tips, Pitfalls & Best Practices

💡 Tip: Use ?? to avoid null checks in simple scenarios.

⚠️ Pitfall: Accessing .Value directly without checking .HasValue causes exceptions.

📘 Best Practice: Always check .HasValue or use safe access patterns like ??.

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📊 Nullable Type Features Summary

Feature	Syntax	Description
Nullable declaration	int? x = null;	Allows null in value types
Null check	x.HasValue	Returns true if not null
Access value	x.Value	Retrieves value (unsafe if null)
Default fallback	x ?? defaultValue	Uses default if null
Safe access	x?.ToString()	Null-safe call on a nullable

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📌 Summary – Recap & Next Steps

Nullable types allow value types to represent the absence of a value, which is useful in data-driven applications and user input validation.

🔍 Key Takeaways:

• Use ? to make value types nullable (int?, bool?)
• Use .HasValue or ?? to avoid exceptions
• Useful in APIs, databases, forms, and optionals

⚙️ Coming up: Dive into 📦 C# Booleans to handle true/false logic in your applications.

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❓ FAQ – C# Nullables

❓ What is a nullable type in C#?
✅ A nullable type (int?, bool?) allows a value type to hold a null value.

❓ How do I check if a nullable has a value?
✅ Use .HasValue or compare against null.

❓ What happens if I access .Value on a null?
❌ It throws an InvalidOperationException.

❓ What is the use of ?? operator?
✅ It provides a default value if the variable is null, e.g., x ?? 0.

❓ Are reference types automatically nullable?
✅ Yes, but in C# 8.0+ with nullable reference types enabled, they can be explicitly marked as nullable with ?.

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