Base keyword behavior in C Sharp (C#) - Mini Project: Build & Apply

Base Keyword Behavior

📖 Scenario: Imagine you are creating a simple program to understand how a child class can use and extend the behavior of its parent class in C#.

🎯 Goal: You will build two classes: a parent class called Animal with a method Speak(), and a child class called Dog that overrides Speak() but also calls the parent class's Speak() method using the base keyword.

📋 What You'll Learn

Create a class Animal with a method Speak() that prints "Animal speaks"

Create a class Dog that inherits from Animal

Override the Speak() method in Dog to first call base.Speak() and then print "Dog barks"

Create an instance of Dog and call its Speak() method to see both messages

💡 Why This Matters

🌍 Real World

Understanding how child classes can reuse and extend parent class behavior is key in many software designs, like creating different types of animals, vehicles, or user roles.

💼 Career

Many programming jobs require knowledge of inheritance and the <code>base</code> keyword to write clean, reusable, and maintainable code.

1

Create the Animal class with Speak method

Create a class called Animal with a public method Speak() that prints "Animal speaks".

C Sharp (C#)

# Your code here to create class Animal with Speak method

Hint

Use class Animal and inside it define public void Speak() that uses Console.WriteLine.

2

Create Dog class inheriting Animal

Create a class called Dog that inherits from Animal.

C Sharp (C#)

using System;

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

# Your code here to create class Dog inheriting Animal

Hint

Use class Dog : Animal to inherit from Animal.

3

Override Speak method in Dog and call base.Speak()

In the Dog class, add a public method Speak() that calls base.Speak() and then prints "Dog barks".

C Sharp (C#)

using System;

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

class Dog : Animal
{
    # Your code here to override Speak and call base.Speak()
}

Hint

Use public new void Speak() in Dog, call base.Speak(), then print "Dog barks".

4

Create Dog instance and call Speak

Create an instance of Dog called dog and call dog.Speak() to print both messages.

C Sharp (C#)

using System;

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

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

# Your code here to create Dog instance and call Speak

Hint

Create Dog dog = new Dog(); and call dog.Speak(); inside Main().

Practice

1. What does the base keyword do in C#?

easy

A. It creates a new instance of a class.

B. It allows a child class to access members of its parent class.

C. It defines a new class.

D. It deletes an object from memory.

Solution

1. Step 1: Understand the role of base

   The base keyword is used in a child class to refer to its parent class members.

2. Step 2: Identify what base allows

   It allows access to parent class methods, properties, or constructors from the child class.

3. Final Answer:

   It allows a child class to access members of its parent class. -> Option B

4. Quick Check:

   base keyword = access parent members [OK]

Hint: Remember: base = parent class access [OK]

Common Mistakes:

• Confusing base with new instance creation
• Thinking base deletes objects
• Assuming base defines a class

2. Which of the following is the correct way to call a parent class constructor using base in C#?

easy

A. public Child() : base() { }

B. public Child() base() { }

C. public Child() call base() { }

D. public Child() : parent() { }

Solution

1. Step 1: Recall syntax for calling parent constructor

   In C#, to call a parent constructor, use : base() after the child constructor signature.

2. Step 2: Match correct syntax

   public Child() : base() { } uses public Child() : base() { }, which is the correct syntax.

3. Final Answer:

   public Child() : base() { } -> Option A

4. Quick Check:

   Parent constructor call = : base() [OK]

Hint: Use colon and base() after constructor name [OK]

Common Mistakes:

• Omitting colon before base()
• Using base() inside constructor body incorrectly
• Using wrong keyword like parent()

3. What will be the output of the following code?

class Parent {
    public virtual void Show() {
        Console.WriteLine("Parent Show");
    }
}
class Child : Parent {
    public override void Show() {
        base.Show();
        Console.WriteLine("Child Show");
    }
}

var obj = new Child();
obj.Show();

medium

A. Child Show

B. Parent Show

C. Compilation error

D. Parent Show\nChild Show

Solution

1. Step 1: Understand method overriding and base call

   The Child class overrides Show() and calls base.Show() which runs the Parent version first.

2. Step 2: Trace the output

   First, "Parent Show" is printed from base.Show(), then "Child Show" is printed from the child method.

3. Final Answer:

   Parent Show Child Show -> Option D

4. Quick Check:

   base.Method() runs parent method first [OK]

Hint: base.Method() runs parent method inside override [OK]

Common Mistakes:

• Ignoring base.Show() call
• Expecting only child output
• Thinking code causes error

4. Identify the error in this code snippet:

class Parent {
    public void Display() {
        Console.WriteLine("Parent Display");
    }
}
class Child : Parent {
    public override void Display() {
        base.Display();
        Console.WriteLine("Child Display");
    }
}

medium

A. Cannot override non-virtual method Display() in Parent.

B. base.Display() is invalid syntax.

C. Child class must not call base.Display().

D. No error, code runs fine.

Solution

1. Step 1: Check method overriding rules

   In C#, only methods marked virtual or abstract in the parent can be overridden.

2. Step 2: Analyze the Parent class method

   The Display() method in Parent is not virtual, so override in Child causes a compile error.

3. Final Answer:

   Cannot override non-virtual method Display() in Parent. -> Option A

4. Quick Check:

   Override requires virtual method [OK]

Hint: Only virtual methods can be overridden [OK]

Common Mistakes:

• Trying to override non-virtual method
• Confusing base call syntax
• Assuming override works without virtual

5. Given the classes below, what will be the output?

class A {
    public virtual string GetName() => "A";
}
class B : A {
    public override string GetName() => "B";
}
class C : B {
    public override string GetName() => base.GetName() + "C";
}

var obj = new C();
Console.WriteLine(obj.GetName());

hard

A. AC

B. Compilation error

C. BC

D. C

Solution

1. Step 1: Trace method calls through inheritance

   Class C overrides GetName() and calls base.GetName(), which refers to B's override returning "B".

2. Step 2: Combine returned strings

   C appends "C" to the result from B, so the final string is "B" + "C" = "BC".

3. Final Answer:

   BC -> Option C

4. Quick Check:

   base.GetName() calls immediate parent method [OK]

Hint: base calls immediate parent method, not grandparent [OK]

Common Mistakes:

• Assuming base calls grandparent method
• Ignoring string concatenation
• Expecting only "C" output