Why encapsulation is required in C++ - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a private member variable in a class.

C++

class Box {
private:
    int [1];
};

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

Aclass

Bpublic

Clength

Dvoid

Attempts:

3 left

💡 Hint

Common Mistakes

Using access specifiers like 'public' as variable names.

The private member variable length is declared inside the class to hide it from outside access.

2fill in blank

medium

Complete the code to provide a public method to access the private variable.

C++

class Box {
private:
    int length;
public:
    int [1]() {
        return length;
    }
};

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

AgetLength

BsetLength

Clength

DBox

Attempts:

3 left

💡 Hint

Common Mistakes

Using the variable name itself as the method name without 'get' prefix.

The method getLength is a public getter that allows controlled access to the private variable length.

3fill in blank

hard

Fix the error in the code to prevent direct access to the private variable.

C++

int main() {
    Box box;
    // box.length = 10; // Error: cannot access private member
    box.[1](10);
    return 0;
}

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

ABox

Blength

CgetLength

DsetLength

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to access the private variable directly.

Using the public setter method setLength allows setting the private variable length safely.

4fill in blank

hard

Fill both blanks to complete the setter method for the private variable.

C++

class Box {
private:
    int length;
public:
    void [1](int [2]) {
        length = [2];
    }
};

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

AsetLength

Bvalue

Clength

DgetLength

Attempts:

3 left

💡 Hint

Common Mistakes

Using the private variable name as the parameter name without distinction.

The setter method setLength takes a parameter value to assign to the private variable length.

5fill in blank

hard

Fill all three blanks to create a class demonstrating encapsulation with private variable and public getter and setter.

C++

class Box {
private:
    int [1];
public:
    void [2](int [3]) {
        length = [3];
    }
    int getLength() {
        return length;
    }
};

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

Alength

BsetLength

Cvalue

DgetLength

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up method names or parameter names.

This class uses encapsulation by keeping length private and providing public methods setLength and getLength to access it safely.

Practice

1. Why is encapsulation important in C++ programming?

easy

A. It hides the internal data to protect it from outside access.

B. It makes the program run faster by using less memory.

C. It allows multiple inheritance in classes.

D. It automatically generates user interfaces.

Solution

1. Step 1: Understand encapsulation concept

   Encapsulation means hiding internal data from outside code to protect it.

2. Step 2: Match with options

   It hides the internal data to protect it from outside access. correctly states that encapsulation hides data to protect it.

3. Final Answer:

   It hides the internal data to protect it from outside access. -> Option A

4. Quick Check:

   Encapsulation = Data protection [OK]

Hint: Encapsulation means hiding data safely [OK]

Common Mistakes:

• Confusing encapsulation with inheritance
• Thinking encapsulation improves speed
• Believing encapsulation creates UI automatically

2. Which of the following is the correct way to declare a private data member in a C++ class?

easy

A. private:
int data;

B. int private data;

C. private int data;

D. int data; private;

Solution

1. Step 1: Recall C++ private section syntax

   In C++, private members are declared under the keyword 'private:' followed by members.

2. Step 2: Check options for correct syntax

   private: int data; shows 'private:' followed by 'int data;', which is correct.

3. Final Answer:

   private: int data; -> Option A

4. Quick Check:

   Private members use 'private:' label [OK]

Hint: Private members go under 'private:' label [OK]

Common Mistakes:

• Placing 'private' before type incorrectly
• Using 'int private data;' which is invalid
• Putting 'private:' after member declaration

3. Consider this C++ class:

#include <iostream>
class Box {
private:
  int length;
public:
  void setLength(int len) { length = len; }
  int getLength() { return length; }
};

int main() {
  Box b;
  b.setLength(10);
  std::cout << b.getLength();
  return 0;
}

What is the output when this program runs?

medium

A. length

B. 10

C. 0

D. Compilation error

Solution

1. Step 1: Analyze setLength method call

   The method setLength(10) sets the private member length to 10.

2. Step 2: Analyze getLength output

   getLength() returns the value of length, which is now 10, so it prints 10.

3. Final Answer:

   10 -> Option B

4. Quick Check:

   Setter sets 10, getter returns 10 [OK]

Hint: Setter sets value, getter returns it [OK]

Common Mistakes:

• Expecting 'length' string output
• Thinking private member can't be accessed
• Assuming default value 0 is printed

4. What is wrong with this C++ code snippet related to encapsulation?

#include <iostream>
class Person {
private:
  int age;
public:
  void setAge(int a) { age = a; }
  int getAge() { return age; }
};

int main() {
  Person p;
  p.age = 25;
  std::cout << p.getAge();
  return 0;
}

medium

A. Getter method getAge() should be private.

B. Missing semicolon after class definition.

C. Direct access to private member 'age' is not allowed.

D. setAge method should return int.

Solution

1. Step 1: Identify access to private member

   The code tries to assign p.age = 25; but age is private, so direct access is illegal.

2. Step 2: Check other options

   Class ends with semicolon, getAge is public correctly, setAge can be void. So only direct access is wrong.

3. Final Answer:

   Direct access to private member 'age' is not allowed. -> Option C

4. Quick Check:

   Private members cannot be accessed directly [OK]

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

Common Mistakes:

• Trying to access private data directly
• Thinking getter should be private
• Assuming setAge must return a value

5. You want to protect a class's data but still allow controlled access. Which encapsulation approach is best in C++?

hard

A. Make data protected and never provide any access functions.

B. Make data public and use comments to warn users not to change it.

C. Use global variables instead of class members.

D. Make data private and provide public getter and setter functions.

Solution

1. Step 1: Understand encapsulation goal

   Encapsulation protects data by hiding it and controlling access through functions.

2. Step 2: Evaluate options for best practice

   Make data private and provide public getter and setter functions. uses private data with public getter/setter, which is standard and safe.

3. Final Answer:

   Make data private and provide public getter and setter functions. -> Option D

4. Quick Check:

   Private data + public methods = Encapsulation [OK]

Hint: Private data + public methods = safe access [OK]

Common Mistakes:

• Making data public and trusting comments
• Using global variables instead of encapsulation
• Not providing any access to data