Do local bool variables have default values in C#?

No, local variables must be initialized before use or it will cause a compile-time error.

What is the Default Value of a Boolean in C#? | FullStackPrep.Dev

Q: What is the default value of a boolean in C#?

The default value of a bool in C# is false when declared as a field, array element, or class member.

💡 Concept: Default Boolean Value

In C#, the bool data type represents a binary condition: true or false. Its default value is false, unless explicitly initialized.

📘 Quick Intro

The default value of a boolean field or array element in C# is false. However, local variables must be assigned before use.

🧠 Analogy

Imagine a light switch. When a new switch is installed in a room and never turned on, it starts off as off—not emitting any light. Similarly, in C#, a bool is false by default, representing an “off” or untriggered state.

🔧 Technical Explanation

bool is a value type (System.Boolean) and stores either true or false.
Its default value is false when declared as a field, struct member, or array element.
Local variables do not get a default value—you must assign them before using.
Static fields and class-level fields are automatically initialized to false.
Nullable boolean (bool?) has a default of null, not false.

🎯 Use Cases

Use default boolean for flags like isActive, isLoggedIn, etc.
Boolean arrays default to all false.
Use default values in model validation and condition handling.

💻 C# Code Example

public class User {
    public bool IsVerified;  // default is false
}

public class Program {
    static void Main() {
        User u = new User();
        Console.WriteLine(u.IsVerified);  // Output: false
    }
}

❓ Interview Q&A

Q1: What is the default value of a bool in C#?
A: false

Q2: Do local bool variables have default values?
A: No, they must be initialized before use.

Q3: What is the default value of a bool array element?
A: false

Q4: What happens if a local bool is used uninitialized?
A: It causes a compile-time error.

Q5: What is the default for a bool? nullable bool?
A: null

Q6: Are static boolean fields auto-initialized?
A: Yes, to false

Q7: Can the default value of bool be changed?
A: No, but you can initialize it explicitly.

Q8: How do you explicitly set a bool to true?
A: Use assignment: flag = true;

Q9: Is bool a reference or value type?
A: It's a value type.

Q10: Can bool be null in C#?
A: Only if declared as nullable (i.e., bool?).

📝 MCQs

Q1. What is the default value of a bool in C#?

true
false
null
0

Q2. Do local variables of type bool have default values?

Yes
No
Sometimes
Only in structs

Q3. What is the default of a bool[] array?

true
null
false
undefined

Q4. What is the default of a nullable bool?

false
true
null
undefined

Q5. What will Console.WriteLine(new bool()); print?

True
False
Null
Error

Q6. Can you assign null to a bool?

Yes
No
Only in arrays
Only at runtime

Q7. Which type does bool derive from?

System.Object
System.ReferenceType
System.ValueType
System.Primitive

Q8. Can static bool fields be uninitialized?

Yes, default is true
Yes, default is false
No
Only in classes

Q9. How to explicitly assign true to a bool?

flag := true;
flag = 1;
flag = true;
flag.set(true);

Q10. What is the size of bool in C#?

1 byte
4 bytes
2 bits
64 bits

💡 Bonus Insight

Boolean default values are foundational for building logic around system states. Understanding when and how they are initialized prevents unnecessary bugs in class-level declarations or array manipulations.

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What is the Default Value of a Boolean in C#?