Function overriding in C++ - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a base class function that can be overridden.

C++

class Base {
public:
    virtual void [1]() {
        std::cout << "Base function" << std::endl;
    }
};

Drag options to blanks, or click blank then click option'

Arun

Bshow

Cprint

Ddisplay

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different function name that does not match the derived class function.

The function name display is used in the base class and will be overridden in the derived class.

2fill in blank

medium

Complete the code to override the base class function in the derived class.

C++

class Derived : public Base {
public:
    void [1]() override {
        std::cout << "Derived function" << std::endl;
    }
};

Drag options to blanks, or click blank then click option'

Aprint

Bdisplay

Cshow

Drun

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different function name or missing the override keyword.

The derived class overrides the display function from the base class.

3fill in blank

hard

Fix the error in the base class function declaration to allow overriding.

C++

class Base {
public:
    virtual void [1]() {
        std::cout << "Base function" << std::endl;
    }
};

Drag options to blanks, or click blank then click option'

Arun

Bshow

Cdisplay

Dprint

Attempts:

3 left

💡 Hint

Common Mistakes

Changing the function name so it does not match the derived class.

The base class function must be declared virtual to allow overriding, but here the blank is the function name which must be display to match derived class.

4fill in blank

hard

Fill both blanks to complete the derived class overriding the base class function.

C++

class Derived : public Base {
public:
    [1] [2]() override {
        std::cout << "Derived override" << std::endl;
    }
};

Drag options to blanks, or click blank then click option'

Avoid

Bint

Cdisplay

Dshow

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different return type or function name.

The function must have the same return type void and the same name display as in the base class to override it.

5fill in blank

hard

Fill all three blanks to call the overridden function through a base class pointer.

C++

Base* ptr = new Derived();
ptr->[1]();
delete [2];
[3] = nullptr;

Drag options to blanks, or click blank then click option'

Aptr

Bdisplay

DbasePtr

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong pointer names or function names.

We call the overridden function display through the base class pointer ptr, then delete and nullify the pointer.

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