Base class and derived class in C Sharp (C#) - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of base and derived class method calls

What is the output of the following C# code?

C Sharp (C#)

using System;

class Animal {
    public virtual void Speak() {
        Console.WriteLine("Animal speaks");
    }
}

class Dog : Animal {
    public override void Speak() {
        Console.WriteLine("Dog barks");
    }
}

class Program {
    static void Main() {
        Animal a = new Animal();
        Animal b = new Dog();
        Dog d = new Dog();

        a.Speak();
        b.Speak();
        d.Speak();
    }
}

A

Animal speaks
Animal speaks
Dog barks

B

Animal speaks
Dog barks
Animal speaks

C

Animal speaks
Dog barks
Dog barks

D

Dog barks
Dog barks
Dog barks

💡 Hint

Remember that virtual methods allow derived classes to override behavior.

The base class method Speak is virtual and overridden in Dog. When calling Speak on a base class reference to a Dog object, the Dog's override is called.

❓ Predict Output

intermediate

Output when base class constructor calls virtual method

What is the output of this C# program?

C Sharp (C#)

using System;

class Base {
    public Base() {
        Print();
    }
    public virtual void Print() {
        Console.WriteLine("Base Print");
    }
}

class Derived : Base {
    private int x = 5;
    public override void Print() {
        Console.WriteLine($"Derived Print: x = {x}");
    }
}

class Program {
    static void Main() {
        Derived d = new Derived();
    }
}

A Derived Print: x = 5

B Derived Print: x = 0

C Base Print

D Compilation error

💡 Hint

Think about the order of initialization when base constructor calls a virtual method.

During base class constructor execution, derived class fields are not yet initialized, so x is 0 (default int).

🔧 Debug

advanced

Why does this derived class method not override base method?

The following code compiles but does not produce the expected output. Why?

C Sharp (C#)

using System;

class Base {
    public void Show() {
        Console.WriteLine("Base Show");
    }
}

class Derived : Base {
    public void Show() {
        Console.WriteLine("Derived Show");
    }
}

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

A Because the base class method is not marked virtual, so the derived method hides it but does not override.

B Because the derived class method has a different name and signature.

C Because the base class method is private and cannot be overridden.

D Because the derived class method is static and cannot override instance methods.

💡 Hint

Check if the base method is virtual or not.

Only virtual methods can be overridden. Here, Show in Base is not virtual, so Derived.Show hides it but does not override. The call uses Base's method.

📝 Syntax

advanced

Which option causes a compile-time error?

Which of the following code snippets will cause a compile-time error in C#?

A class Base { public virtual void Foo() {} } class Derived : Base { public override void Foo() {} }

B class Base { public virtual void Foo() {} } class Derived : Base { public void Foo() {} }

C class Base { public virtual void Foo() {} } class Derived : Base { public new void Foo() {} }

D class Base { public void Foo() {} } class Derived : Base { public override void Foo() {} }

💡 Hint

Override keyword requires the base method to be virtual or abstract.

Option D tries to override a non-virtual method, causing a compile-time error.

🚀 Application

expert

Number of accessible members in derived class instance

Given the classes below, how many members (methods and properties) can be accessed directly from an instance of Derived?

C Sharp (C#)

class Base {
    public void PublicMethod() {}
    protected void ProtectedMethod() {}
    private void PrivateMethod() {}
    public int PublicProperty { get; set; }
    protected int ProtectedProperty { get; set; }
    private int PrivateProperty { get; set; }
}

class Derived : Base {
    public void DerivedMethod() {}
    public int DerivedProperty { get; set; }
}

// In Main:
// Derived d = new Derived();
// How many members can be accessed via d. ?

A 4

B 5

C 6

D 7

💡 Hint

Remember that private members of base class are not accessible in derived class instances.

Accessible members are: PublicMethod, PublicProperty, DerivedMethod, DerivedProperty, and Protected members are NOT accessible via instance outside class, so total 4.