Protected access modifier in C Sharp (C#) - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of accessing protected member in derived class

What is the output of this C# code when run?

C Sharp (C#)

class Animal {
    protected string sound = "Roar";
}

class Lion : Animal {
    public void MakeSound() {
        System.Console.WriteLine(sound);
    }
}

class Program {
    static void Main() {
        Lion lion = new Lion();
        lion.MakeSound();
    }
}

A Roar

B Compilation error: 'sound' is inaccessible due to its protection level

C Runtime error: NullReferenceException

D No output

💡 Hint

Remember that protected members are accessible in derived classes.

The protected member 'sound' is accessible inside the derived class Lion, so printing it works and outputs 'Roar'.

❓ Predict Output

intermediate

Accessing protected member from outside derived class

What happens when this C# code is compiled?

C Sharp (C#)

class Vehicle {
    protected int speed = 100;
}

class Car : Vehicle {
}

class Program {
    static void Main() {
        Vehicle v = new Vehicle();
        System.Console.WriteLine(v.speed);
    }
}

A Compilation error: 'speed' is inaccessible due to its protection level

B No output

C 100

D Runtime error: NullReferenceException

💡 Hint

Protected members are not accessible from outside the class or its derived classes.

The 'speed' field is protected, so it cannot be accessed from an instance of Vehicle outside the class or derived classes, causing a compilation error.

🔧 Debug

advanced

Why does this code cause a compilation error?

This code tries to access a protected member from an unrelated class. What is the cause of the compilation error?

C Sharp (C#)

class Parent {
    protected int number = 42;
}

class Child : Parent {
}

class Stranger {
    void ShowNumber() {
        Parent p = new Parent();
        System.Console.WriteLine(p.number);
    }
}

A The 'number' field is private, so it cannot be accessed outside Parent.

B The 'Parent' class must be declared as public to access its members.

C Protected members can only be accessed within the class or its derived classes, not from unrelated classes.

D The 'ShowNumber' method is not static, causing the error.

💡 Hint

Think about who can access protected members.

Protected members are accessible only inside the class and its subclasses. The 'Stranger' class is unrelated and cannot access 'number'.

❓ Predict Output

advanced

Output when accessing protected member via derived class reference

What is the output of this C# program?

C Sharp (C#)

class Base {
    protected string message = "Hello from Base";
}

class Derived : Base {
    public void PrintMessage() {
        System.Console.WriteLine(message);
    }
}

class Program {
    static void Main() {
        Base b = new Derived();
        ((Derived)b).PrintMessage();
    }
}

A Compilation error: Cannot convert Base to Derived

B Hello from Base

C Runtime error: InvalidCastException

D No output

💡 Hint

Casting to the derived type allows access to its methods.

The object is actually a Derived instance, so casting to Derived and calling PrintMessage works and prints the protected member.

🧠 Conceptual

expert

Understanding protected access in nested classes

Consider this C# code. What is the output when running Main?

C Sharp (C#)

class Outer {
    protected int value = 10;
    public class Inner : Outer {
        public void ShowValue() {
            System.Console.WriteLine(value);
        }
    }
}

class Program {
    static void Main() {
        Outer.Inner inner = new Outer.Inner();
        inner.ShowValue();
    }
}

A No output

B Compilation error: 'value' is inaccessible due to its protection level

C Runtime error: NullReferenceException

D 10

💡 Hint

Nested classes can inherit and access protected members of the outer class.

Inner inherits from Outer and can access the protected member 'value', so it prints 10.

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