Protected access modifier in C Sharp (C#) - Mini Project: Build & Apply

Understanding the Protected Access Modifier in C#

📖 Scenario: Imagine you are creating a simple program to manage vehicles. You want to keep some details safe inside the vehicle class but still allow special access to classes that inherit from it.

🎯 Goal: Build a small C# program that uses the protected access modifier to allow a child class to access a parent's protected member.

📋 What You'll Learn

Create a base class called Vehicle with a protected string variable brand set to "Toyota"

Create a derived class called Car that inherits from Vehicle

Inside Car, create a method ShowBrand that returns the brand value

In the Main method, create an object of Car and print the result of ShowBrand()

💡 Why This Matters

🌍 Real World

Protected members help keep important data safe inside a class but still allow child classes to use or modify it. This is common in software that models real-world objects with inheritance.

💼 Career

Understanding access modifiers like protected is essential for writing clean, secure, and maintainable object-oriented code in professional C# development.

1

Create the base class with a protected member

Create a class called Vehicle with a protected string variable brand set to "Toyota".

C Sharp (C#)

// Your code here

Hint

Use the keyword protected before the variable brand inside the Vehicle class.

2

Create a derived class that inherits Vehicle

Create a class called Car that inherits from Vehicle. Inside Car, create a method ShowBrand that returns the brand variable.

C Sharp (C#)

class Vehicle
{
    protected string brand = "Toyota";
}
// Your code here

Hint

Use class Car : Vehicle to inherit. The method ShowBrand should return the protected brand variable.

3

Create the Main method and instantiate Car

Create a Main method inside a Program class. Inside Main, create an object of Car called myCar.

C Sharp (C#)

class Vehicle
{
    protected string brand = "Toyota";
}

class Car : Vehicle
{
    public string ShowBrand()
    {
        return brand;
    }
}

// Your code here

Hint

Define a Program class with a Main method. Inside Main, create myCar as a new Car object.

4

Print the brand using ShowBrand method

Inside the Main method, use Console.WriteLine to print the result of myCar.ShowBrand().

C Sharp (C#)

class Vehicle
{
    protected string brand = "Toyota";
}

class Car : Vehicle
{
    public string ShowBrand()
    {
        return brand;
    }
}

class Program
{
    static void Main()
    {
        Car myCar = new Car();
        // Your code here
    }
}

Hint

Use Console.WriteLine(myCar.ShowBrand()); to print the brand.

Practice

1.

What does the protected access modifier mean in C#?

easy

A. Only the class itself and its subclasses can access the member.

B. Any code in the same assembly can access the member.

C. Only code outside the class can access the member.

D. The member is accessible everywhere without restriction.

Solution

1. Step 1: Understand the meaning of protected

   The protected modifier restricts access to the class itself and any classes that inherit from it.

2. Step 2: Compare with other access levels

   Unlike public or internal, protected hides members from outside classes except subclasses.

3. Final Answer:

   Only the class itself and its subclasses can access the member. -> Option A

4. Quick Check:

   Protected = class + subclasses access [OK]

Hint: Protected means class and subclasses only [OK]

Common Mistakes:

• Confusing protected with public
• Thinking protected allows access from unrelated classes
• Mixing protected with internal or private

2.

Which of the following is the correct way to declare a protected method named Calculate in C#?

?

easy

A. internal void Calculate() { }

B. private void Calculate() { }

C. public void Calculate() { }

D. protected void Calculate() { }

Solution

1. Step 1: Recall protected method syntax

   In C#, the keyword protected is used before the return type to declare a protected method.

2. Step 2: Check each option

   protected void Calculate() { } uses protected void Calculate(), which is correct syntax for a protected method.

3. Final Answer:

   protected void Calculate() { } -> Option D

4. Quick Check:

   Protected method syntax = protected + return type [OK]

Hint: Protected methods start with 'protected' keyword [OK]

Common Mistakes:

• Using private or public instead of protected
• Omitting the return type
• Placing protected after the method name

3.

Consider the following code:

class Parent {
    protected int number = 5;
}

class Child : Parent {
    public int GetNumber() {
        return number;
    }
}

class Program {
    static void Main() {
        Child c = new Child();
        Console.WriteLine(c.GetNumber());
    }
}

What will be the output when this program runs?

medium

A. 0

B. 5

C. Compilation error

D. Runtime error

Solution

1. Step 1: Understand protected member access in subclass

   The number field is protected, so the subclass Child can access it directly.

2. Step 2: Trace the program output

   The GetNumber method returns number which is 5, so Console.WriteLine prints 5.

3. Final Answer:

   5 -> Option B

4. Quick Check:

   Protected field accessed in subclass = 5 [OK]

Hint: Protected members accessible in subclass methods [OK]

Common Mistakes:

• Thinking protected means inaccessible outside parent
• Expecting compilation error due to access
• Confusing protected with private

4.

Identify the error in this code snippet:

class Base {
    protected int value = 10;
}

class Other {
    void Show() {
        Base b = new Base();
        Console.WriteLine(b.value);
    }
}

medium

A. Class Other must inherit Base to access value.

B. Missing semicolon after declaration.

C. Cannot access protected member from unrelated class instance.

D. No error, code runs fine.

Solution

1. Step 1: Check access of protected member from unrelated class

   The class Other does not inherit from Base, so it cannot access value which is protected.

2. Step 2: Understand protected access rules

   Protected members are accessible only within the class and its subclasses, not from unrelated classes.

3. Final Answer:

   Cannot access protected member from unrelated class instance. -> Option C

4. Quick Check:

   Protected access = class + subclasses only [OK]

Hint: Protected not accessible from unrelated classes [OK]

Common Mistakes:

• Assuming protected is like public
• Thinking inheritance is not required
• Ignoring access modifier rules

5.

You want to create a base class Vehicle with a protected field speed. You also want a subclass Car that can set and get this speed, but no other class should access it directly. Which code snippet correctly implements this?

hard

A. class Vehicle { protected int speed; }
class Car : Vehicle {
public void SetSpeed(int s) { speed = s; }
public int GetSpeed() { return speed; }
}

B. class Vehicle { public int speed; }
class Car : Vehicle { }
// Any class can access speed directly

C. class Vehicle { private int speed; }
class Car : Vehicle {
public int GetSpeed() { return speed; }
}

D. class Vehicle { internal int speed; }
class Car : Vehicle { }
// speed accessible only in same assembly

Solution

1. Step 1: Use protected field in base class

   The field speed is declared protected in Vehicle so only Vehicle and subclasses can access it.

2. Step 2: Provide public methods in subclass to access speed

   The subclass Car has public methods SetSpeed and GetSpeed to safely access the protected field.

3. Step 3: Check other options for access control

   class Vehicle { public int speed; } class Car : Vehicle { } // Any class can access speed directly uses public field, which allows all classes to access speed directly. class Vehicle { private int speed; } class Car : Vehicle { public int GetSpeed() { return speed; } } uses private field, so subclass cannot access it. class Vehicle { internal int speed; } class Car : Vehicle { } // speed accessible only in same assembly uses internal, which restricts access to assembly, not subclasses.

4. Final Answer:

   class Vehicle { protected int speed; } class Car : Vehicle { public void SetSpeed(int s) { speed = s; } public int GetSpeed() { return speed; } } -> Option A

5. Quick Check:

   Protected field + subclass methods = correct encapsulation [OK]

Hint: Protected field with public subclass methods controls access [OK]

Common Mistakes:

• Using public field exposing speed to all
• Using private field inaccessible to subclass
• Confusing internal with protected