OOP principles overview in C++ - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a class named Car.

C++

class [1] {
public:
    void drive() {}
};

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

ACar

BVehicle

CDrive

DEngine

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different class name than requested.

The class name should be Car as specified.

2fill in blank

medium

Complete the code to create an object named myCar of class Car.

C++

Car [1];

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

AmyCar

Bdrive

CCar

Dvehicle

Attempts:

3 left

💡 Hint

Common Mistakes

Using the class name instead of the object name.

The object name should be myCar as requested.

3fill in blank

hard

Fix the error in the code to access the drive method using the object myCar.

C++

myCar.[1]();

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

Adrives

BDrive

Cdrive

DdriveCar

Attempts:

3 left

💡 Hint

Common Mistakes

Capitalizing the method name incorrectly.

The method name is drive exactly as declared in the class.

4fill in blank

hard

Fill both blanks to define a class Person with a private age and a public method to get age.

C++

class Person {
private:
    int [1];
public:
    int [2]() { return age; }
};

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

Aage

BgetAge

CsetAge

DageValue

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong variable or method names.

The private variable is named age and the public method to get it is getAge.

5fill in blank

hard

Fill all three blanks to implement inheritance where Student inherits from Person and adds a method to get grade.

C++

class Student : public [1] {
public:
    int [2]() { return grade; }
private:
    int [3];
};

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

APerson

BgetGrade

Cgrade

DStudent

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong base class or method names.

Student inherits from Person. It has a method getGrade and a private variable grade.

Practice

1. Which of the following is NOT one of the four main principles of Object-Oriented Programming (OOP)?

easy

A. Encapsulation

B. Compilation

C. Polymorphism

D. Inheritance

Solution

1. Step 1: Recall the four main OOP principles

   The four main principles are encapsulation, inheritance, polymorphism, and abstraction.

2. Step 2: Identify the option not in the list

   Compilation is a process of converting code, not an OOP principle.

3. Final Answer:

   Compilation -> Option B

4. Quick Check:

   OOP principles exclude compilation [OK]

Hint: Remember the four OOP pillars: E, I, P, A [OK]

Common Mistakes:

• Confusing compilation with abstraction
• Mixing OOP principles with programming processes

2. Which keyword is used in C++ to create a new class?

easy

A. class

B. struct

C. object

D. define

Solution

1. Step 1: Identify the C++ keyword for defining a class

   In C++, the keyword to define a class is class.

2. Step 2: Check other options

   struct defines a structure, object is not a keyword, and define is for macros.

3. Final Answer:

   class -> Option A

4. Quick Check:

   Use class to define classes [OK]

Hint: Use 'class' keyword to define classes in C++ [OK]

Common Mistakes:

• Confusing struct with class
• Using 'object' as a keyword
• Mixing macros with class definition

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

class Animal {
public:
    void sound() { std::cout << "Animal sound"; }
};

class Dog : public Animal {
public:
    void sound() { std::cout << "Bark"; }
};

int main() {
    Animal* a = new Dog();
    a->sound();
    delete a;
    return 0;
}

medium

A. Runtime error

B. Bark

C. Compilation error

D. Animal sound

Solution

1. Step 1: Understand method call without virtual keyword

   The sound method is not virtual, so the pointer type Animal* calls Animal's method.

2. Step 2: Determine output

   Since sound is not virtual, Animal sound is printed.

3. Final Answer:

   Animal sound -> Option D

4. Quick Check:

   Non-virtual method calls base class method [OK]

Hint: Without virtual, base class method runs [OK]

Common Mistakes:

• Assuming polymorphism without virtual
• Expecting derived class method call
• Ignoring pointer type effect

4. Identify the error in the following C++ code snippet:

class Vehicle {
private:
    int speed;
public:
    void setSpeed(int s) { speed = s; }
};

int main() {
    Vehicle v;
    v.speed = 100;
    return 0;
}

medium

A. setSpeed method is not defined

B. Missing semicolon after class definition

C. Cannot access private member 'speed' directly

D. Vehicle object not created properly

Solution

1. Step 1: Check access to private member

   The member speed is private and cannot be accessed directly outside the class.

2. Step 2: Identify the error in main()

   Trying to assign v.speed = 100; causes an access violation error.

3. Final Answer:

   Cannot access private member 'speed' directly -> Option C

4. Quick Check:

   Private members need public methods for access [OK]

Hint: Private members can't be accessed outside class [OK]

Common Mistakes:

• Trying to access private variables directly
• Ignoring access specifiers
• Assuming public by default

5. You want to design a C++ class hierarchy where a base class Shape defines a method area() but each derived class calculates area differently. Which OOP principle does this best demonstrate?

hard

A. Polymorphism

B. Inheritance

C. Encapsulation

D. Abstraction

Solution

1. Step 1: Understand the scenario of different area calculations

   Each derived class implements area() differently, but shares the same interface.

2. Step 2: Identify the OOP principle

   This is polymorphism: same method name, different behaviors in subclasses.

3. Final Answer:

   Polymorphism -> Option A

4. Quick Check:

   Same method, different behaviors = Polymorphism [OK]

Hint: Different behaviors, same method name = polymorphism [OK]

Common Mistakes:

• Confusing with inheritance or abstraction
• Thinking encapsulation means method overriding