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.