Method overriding with virtual and override in C Sharp (C#) - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of overridden method call

What is the output of this C# program?

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 Dog();
        a.Speak();
    }
}

A Animal speaks

B Runtime exception

C Compile-time error

D Dog barks

💡 Hint

Remember that virtual methods allow derived classes to provide their own implementation.

The variable a is of type Animal but refers to a Dog object. Because Speak is virtual and overridden in Dog, the Dog version runs, printing "Dog barks".

❓ Predict Output

intermediate

Output when base method is not virtual

What will this program print?

C Sharp (C#)

using System;
class Base {
    public void Show() {
        Console.WriteLine("Base Show");
    }
}
class Derived : Base {
    public new void Show() {
        Console.WriteLine("Derived Show");
    }
}
class Program {
    static void Main() {
        Base b = new Derived();
        b.Show();
    }
}

A Base Show

B Derived Show

C Compile-time error

D Runtime exception

💡 Hint

Check if the base method is virtual or not.

The base method Show is not virtual, so the call b.Show() uses the base class method even though b refers to a Derived object.

❓ Predict Output

advanced

Output with multiple overrides and base calls

What is the output of this program?

C Sharp (C#)

using System;
class A {
    public virtual void Print() {
        Console.WriteLine("A");
    }
}
class B : A {
    public override void Print() {
        Console.WriteLine("B");
        base.Print();
    }
}
class C : B {
    public override void Print() {
        Console.WriteLine("C");
        base.Print();
    }
}
class Program {
    static void Main() {
        A obj = new C();
        obj.Print();
    }
}

A

C
B
A

B

A
B
C

C

C
A
B

D

B
C
A

💡 Hint

Follow the calls from the most derived class up to base classes.

The call obj.Print() runs C.Print() which prints "C" then calls B.Print(). B.Print() prints "B" then calls A.Print() which prints "A". So the output is:
C
B
A

❓ Predict Output

advanced

Error when overriding without override keyword

What error does this code produce?

C Sharp (C#)

using System;
class Parent {
    public virtual void Display() {
        Console.WriteLine("Parent Display");
    }
}
class Child : Parent {
    public void Display() {
        Console.WriteLine("Child Display");
    }
}
class Program {
    static void Main() {
        Parent p = new Child();
        p.Display();
    }
}

A Runtime exception: Method not found

B Output: Parent Display

C Compile-time error: Child.Display must use override keyword

D Output: Child Display

💡 Hint

Check if the child method overrides or hides the base method.

The Child.Display method does not use override keyword, so it hides the base method instead of overriding it. The call p.Display() uses the base class method, printing "Parent Display".

🧠 Conceptual

expert

Why use virtual and override keywords?

Which statement best explains why C# uses virtual and override keywords for method overriding?

A To automatically generate base class methods in derived classes

B To make methods run faster by skipping virtual dispatch

C To allow the compiler to check that a derived class method correctly overrides a base class virtual method

D To prevent any method in derived classes from changing base class behavior

💡 Hint

Think about safety and clarity in overriding methods.

The virtual keyword marks a method as overridable. The override keyword tells the compiler that the method is intended to override a base virtual method. This helps catch mistakes like misspelling or wrong signatures.