Function overriding in C++ - Mini Project: Build & Apply

Function overriding

📖 Scenario: Imagine you have a base class Animal that can make a sound. Different animals make different sounds. We want to show how a derived class can change the sound by overriding the base class function.

🎯 Goal: Build a simple C++ program that demonstrates function overriding by creating a base class Animal with a makeSound() function, and a derived class Dog that overrides makeSound() to show a different sound.

📋 What You'll Learn

Create a base class called Animal with a public function makeSound() that prints "Some generic animal sound".

Create a derived class called Dog that inherits from Animal.

Override the makeSound() function in Dog to print "Woof!".

Create an object of Dog and call its makeSound() function to show the overridden behavior.

💡 Why This Matters

🌍 Real World

Function overriding is used in software to allow different objects to behave differently while sharing the same interface. For example, different animals making different sounds in a zoo simulation.

💼 Career

Understanding function overriding is essential for object-oriented programming jobs, especially when working with inheritance and polymorphism in C++.

1

Create the base class Animal with makeSound()

Write a class called Animal with a public function makeSound() that prints exactly "Some generic animal sound" followed by a newline.

C++

// Your code here

Hint

Use class Animal and define void makeSound() inside it. Use std::cout to print the text.

2

Create the derived class Dog that inherits Animal

Add a class called Dog that publicly inherits from Animal. Do not add any functions yet.

C++

#include 

class Animal {
public:
    void makeSound() {
        std::cout << "Some generic animal sound" << std::endl;
    }
};

// Your code here

Hint

Use class Dog : public Animal to create the derived class.

3

Override makeSound() in Dog to print "Woof!"

Inside the Dog class, override the makeSound() function to print exactly "Woof!" followed by a newline.

C++

#include 

class Animal {
public:
    void makeSound() {
        std::cout << "Some generic animal sound" << std::endl;
    }
};

class Dog : public Animal {
    // Your code here
};

Hint

Define void makeSound() inside Dog and print "Woof!" using std::cout.

4

Create Dog object and call makeSound()

In the main() function, create an object called myDog of type Dog and call its makeSound() function.

C++

#include 

class Animal {
public:
    void makeSound() {
        std::cout << "Some generic animal sound" << std::endl;
    }
};

class Dog : public Animal {
public:
    void makeSound() {
        std::cout << "Woof!" << std::endl;
    }
};

int main() {
    // Your code here
    return 0;
}

Hint

Create Dog myDog; and call myDog.makeSound(); inside main().

Practice

1. What is function overriding in C++?

easy

A. A child class provides its own version of a parent class's virtual function.

B. A function with the same name but different parameters in the same class.

C. A function that is called automatically when an object is created.

D. A function that cannot be changed once defined.

Solution

1. Step 1: Understand function overriding concept

   Function overriding means a child class changes the behavior of a function defined in its parent class.

2. Step 2: Identify correct description

   A child class provides its own version of a parent class's virtual function. correctly describes overriding as providing a new version of a parent's virtual function in the child class.

3. Final Answer:

   A child class provides its own version of a parent class's virtual function. -> Option A

4. Quick Check:

   Function overriding = child changes parent's virtual function [OK]

Hint: Overriding means child changes parent's virtual function [OK]

Common Mistakes:

• Confusing overriding with overloading
• Thinking overriding happens without virtual keyword
• Believing overriding applies to non-virtual functions

2. Which of the following is the correct syntax to override a function in C++11 and later?

easy

A. void func() virtual override;

B. override void func();

C. void func() override;

D. virtual void func() override;

Solution

1. Step 1: Recall override syntax in child class

   In C++11+, the child class function uses the same signature and adds the 'override' keyword after the function declaration.

2. Step 2: Identify correct syntax

   virtual void func() override; shows the correct syntax: 'virtual void func() override;'. The 'virtual' keyword can be used in the child class but is optional; however, it is valid and common to include it.

3. Final Answer:

   virtual void func() override; -> Option D

4. Quick Check:

   Child function uses virtual and override keywords correctly [OK]

Hint: Use 'override' after function signature in child class; 'virtual' is optional but allowed [OK]

Common Mistakes:

• Adding 'virtual' keyword after function name
• Placing 'override' before function name
• Omitting 'override' keyword entirely

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

class Base {
public:
    virtual void show() { std::cout << "Base"; }
};
class Derived : public Base {
public:
    void show() override { std::cout << "Derived"; }
};
int main() {
    Base* b = new Derived();
    b->show();
    delete b;
    return 0;
}

medium

A. Derived

B. Base

C. Compilation error

D. Runtime error

Solution

1. Step 1: Understand virtual function behavior

   The pointer 'b' is of type Base* but points to a Derived object. Because 'show' is virtual, the Derived version is called.

2. Step 2: Trace the function call

   Calling b->show() invokes Derived::show(), printing "Derived".

3. Final Answer:

   Derived -> Option A

4. Quick Check:

   Virtual function calls child's version [OK]

Hint: Virtual functions call child's version via base pointer [OK]

Common Mistakes:

• Expecting base class output
• Forgetting to make base function virtual
• Confusing pointer type with object type

4. Identify the error in the following code snippet:

class Parent {
public:
    void display() { std::cout << "Parent"; }
};
class Child : public Parent {
public:
    void display() override { std::cout << "Child"; }
};

medium

A. Child's display() should not use override keyword.

B. Parent's display() must be declared virtual to override.

C. display() must return int, not void.

D. No error, code is correct.

Solution

1. Step 1: Check virtual keyword in parent

   For overriding to work, the base class function must be declared virtual.

2. Step 2: Analyze override keyword usage

   Child uses 'override' but Parent's display() is not virtual, causing a compilation error.

3. Final Answer:

   Parent's display() must be declared virtual to override. -> Option B

4. Quick Check:

   Base function must be virtual for override [OK]

Hint: Base function must be virtual to allow override [OK]

Common Mistakes:

• Ignoring virtual keyword in base class
• Thinking override works without virtual
• Assuming override keyword is optional

5. Given the classes below, what will be the output of obj->print();?

class A {
public:
    virtual void print() { std::cout << "A"; }
};
class B : public A {
public:
    void print() override { std::cout << "B"; }
};
class C : public B {
public:
    void print() override { std::cout << "C"; }
};

int main() {
    A* obj = new C();
    obj->print();
    delete obj;
    return 0;
}

hard

A. A

B. B

C. C

D. Compilation error

Solution

1. Step 1: Understand pointer and object types

   Pointer 'obj' is of type A*, but it points to an object of class C.

2. Step 2: Follow virtual function overriding chain

   Since print() is virtual and overridden in B and C, the most derived override (C::print) is called.

3. Final Answer:

   C -> Option C

4. Quick Check:

   Virtual call resolves to most derived override [OK]

Hint: Virtual calls use most derived override at runtime [OK]

Common Mistakes:

• Expecting base class output
• Confusing pointer type with object type
• Ignoring virtual function behavior