Encapsulation best practices in C++ - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

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

C++

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

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

Apublic

Bage

CgetAge

Dvoid

Attempts:

3 left

💡 Hint

Common Mistakes

Using access specifiers like 'public' as variable names.

The private member variable should be named age to store the person's age.

2fill in blank

medium

Complete the code to define a public getter method for the private variable.

C++

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

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

AgetAge

BsetAge

Cage

DPerson

Attempts:

3 left

💡 Hint

Common Mistakes

Naming the getter method the same as the variable.

The getter method should be named getAge to return the private variable age.

3fill in blank

hard

Fix the error in the setter method to properly set the private variable.

C++

class Person {
private:
    int age;
public:
    void setAge(int [1]) {
        age = [1];
    }
};

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

Avalue

Bage

Cthis

DnewAge

Attempts:

3 left

💡 Hint

Common Mistakes

Using the same name for parameter and member variable without 'this' pointer.

The parameter should have a different name like newAge to avoid confusion and correctly assign the value.

4fill in blank

hard

Fill both blanks to complete the setter method using the 'this' pointer.

C++

class Person {
private:
    int age;
public:
    void setAge(int [1]) {
        this->[2] = [1];
    }
};

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

AnewAge

Bage

Cvalue

DageValue

Attempts:

3 left

💡 Hint

Common Mistakes

Not using 'this->' causing assignment to itself.

The parameter is named newAge and the member variable age is set using this->age.

5fill in blank

hard

Fill all three blanks to create a class with private member, public getter, and setter methods.

C++

class Car {
private:
    int [1];
public:
    int get[2]() {
        return [1];
    }
    void set[2](int value) {
        this->[1] = value;
    }
};

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

Aspeed

BSpeed

Cvelocity

DVelocity

Attempts:

3 left

💡 Hint

Common Mistakes

Using inconsistent names between member and methods.

The private member is speed, the getter and setter use Speed with capital S for method names.

Practice

1. What is the main purpose of encapsulation in C++?

easy

A. To make the program run faster

B. To hide data and protect it from unauthorized access

C. To allow direct access to all class members

D. To increase the size of the program

Solution

1. Step 1: Understand encapsulation concept

   Encapsulation means hiding the internal details of a class to protect data.

2. Step 2: Identify the main goal

   The goal is to prevent wrong or unauthorized changes by restricting direct access.

3. Final Answer:

   To hide data and protect it from unauthorized access -> Option B

4. Quick Check:

   Encapsulation = Data protection [OK]

Hint: Encapsulation means hiding data safely [OK]

Common Mistakes:

• Thinking encapsulation speeds up code
• Believing all data should be public
• Confusing encapsulation with inheritance

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

easy

A. private: int age;

B. int age; // private by default

C. protected int age;

D. public int age;

Solution

1. Step 1: Recall C++ access specifiers

   Private members must be declared after the keyword 'private:' in a class.

2. Step 2: Check each option

   private: int age; uses 'private:' correctly before 'int age;'. Others are either public, protected, or missing specifier.

3. Final Answer:

   private: int age; -> Option A

4. Quick Check:

   Private members use 'private:' label [OK]

Hint: Use 'private:' label before private members [OK]

Common Mistakes:

• Assuming members are private by default
• Using 'private' without colon
• Declaring private members as public

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

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;
}

medium

A. 0

B. Compilation error

C. 10

D. Garbage value

Solution

1. Step 1: Understand class methods

   The method setLength sets the private member length to 10.

2. Step 2: Check output statement

   getLength returns length, which was set to 10, so output is 10.

3. Final Answer:

   10 -> Option C

4. Quick Check:

   Setter sets 10, getter returns 10 [OK]

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

Common Mistakes:

• Expecting default 0 without setting
• Thinking private members can't be accessed via methods
• Confusing compilation error due to private member

4. Identify the error in this C++ class related to encapsulation:

class Person {
public:
    int age;
    void setAge(int a) { age = a; }
    int getAge() { return age; }
};

int main() {
    Person p;
    p.age = -5;
    std::cout << p.getAge();
    return 0;
}

medium

A. Age should be private to prevent invalid values

B. setAge method is missing return type

C. getAge should be private

D. No error, code is correct

Solution

1. Step 1: Check data member access

   Age is public, so it can be set directly to invalid value -5.

2. Step 2: Understand encapsulation best practice

   Age should be private and setAge should validate input to prevent invalid values.

3. Final Answer:

   Age should be private to prevent invalid values -> Option A

4. Quick Check:

   Private data prevents invalid direct changes [OK]

Hint: Make data private to control changes [OK]

Common Mistakes:

• Thinking public data is safe
• Believing getters should be private
• Ignoring validation in setters

5. You want to protect a class's data member balance so it cannot be set to a negative value. Which is the best encapsulation practice to achieve this?

hard

A. Make balance public and check value outside the class

B. Make balance protected and allow derived classes to set it freely

C. Remove balance and use a global variable instead

D. Make balance private and provide a setter that validates input

Solution

1. Step 1: Understand data protection need

   To prevent negative values, direct access must be blocked.

2. Step 2: Use private data with validation

   Making balance private and using a setter method to check values ensures safety.

3. Final Answer:

   Make balance private and provide a setter that validates input -> Option D

4. Quick Check:

   Private data + validated setter = safe encapsulation [OK]

Hint: Use private data and validate in setter [OK]

Common Mistakes:

• Leaving data public for easy access
• Using protected without validation
• Using global variables for encapsulation