Abstract classes in C++ - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare an abstract class with a pure virtual function.

C++

class Shape {
public:
    virtual void draw() [1];
};

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

A()

B{}

C;

D= 0

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting to add = 0 makes the function not pure virtual.

Using empty braces {} defines a normal function, not pure virtual.

In C++, a pure virtual function is declared by assigning = 0 to the function declaration inside the class.

2fill in blank

medium

Complete the code to prevent instantiation of the abstract class.

C++

Shape s; // Error: cannot instantiate abstract class

class Shape {
public:
    virtual void draw() = [1];
};

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A0

B1

Cnull

Dvoid

Attempts:

3 left

💡 Hint

Common Mistakes

Using = 1 or other values instead of = 0.

Trying to instantiate an abstract class causes a compile error.

Assigning = 0 to a virtual function makes the class abstract, so it cannot be instantiated.

3fill in blank

hard

Fix the error in the derived class by correctly overriding the pure virtual function.

C++

class Circle : public Shape {
public:
    void draw() [1] {
        // draw circle
    }
};

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A()

B() override

C(int) override

D(void) override

Attempts:

3 left

💡 Hint

Common Mistakes

Changing the parameter list causes the function not to override.

Omitting override keyword is allowed but not recommended.

The derived class must override the pure virtual function with the exact signature and use override keyword for clarity.

4fill in blank

hard

Fill both blanks to declare an abstract class with a pure virtual destructor and a pure virtual function.

C++

class Interface {
public:
    virtual ~Interface() [1];
    virtual void execute() [2];
};

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A= 0

B{}

C;

D()

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting to define a virtual destructor causes undefined behavior.

Using empty braces {} instead of = 0 does not make the function pure virtual.

Both the destructor and the function are declared pure virtual by assigning = 0.

5fill in blank

hard

Fill all three blanks to implement a derived class that overrides all pure virtual functions and destructor.

C++

class Derived : public Interface {
public:
    ~Derived() [1] override {}
    void execute() [2] override {
        // implementation
    }
    void extra() [3] {
        // extra method
    }
};

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

A()

D(int)

Attempts:

3 left

💡 Hint

Common Mistakes

Changing parameter lists breaks overriding.

Forgetting override keyword can cause silent errors.

All overridden functions must match the base class signature exactly, which is () with no parameters.