Data members and member functions in C++ - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of member function modifying data member

What is the output of this C++ program?

C++

class Counter {
public:
    int count = 0;
    void increment() {
        count++;
    }
};

int main() {
    Counter c;
    c.increment();
    c.increment();
    std::cout << c.count << std::endl;
    return 0;
}

A 2

B 0

C 1

D Compilation error

💡 Hint

The increment function increases the count by one each time it is called.

The count starts at 0. Each call to increment() adds 1. After two calls, count is 2.

❓ Predict Output

intermediate

Output of const member function accessing data member

What will this program print?

C++

class Box {
    int length = 5;
public:
    int getLength() const {
        return length;
    }
};

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

A 5

B 0

C Compilation error due to const function

D Undefined behavior

💡 Hint

Const member functions can read data members but cannot modify them.

The getLength() function returns the value of length which is 5.

❓ Predict Output

advanced

Output when accessing private data member directly

What happens when you try to compile and run this code?

C++

class Sample {
private:
    int value = 10;
public:
    int getValue() {
        return value;
    }
};

int main() {
    Sample s;
    std::cout << s.value << std::endl;
    return 0;
}

A 10

B Runtime error

C 0

D Compilation error: 'value' is private

💡 Hint

Private members cannot be accessed directly outside the class.

The code tries to access private member 'value' directly, which is not allowed.

❓ Predict Output

advanced

Output of static data member shared across objects

What is the output of this program?

C++

class Tracker {
public:
    static int count;
    Tracker() { count++; }
};

int Tracker::count = 0;

int main() {
    Tracker t1;
    Tracker t2;
    Tracker t3;
    std::cout << Tracker::count << std::endl;
    return 0;
}

A 0

B 3

C 1

D Compilation error due to static member

💡 Hint

Static members are shared by all objects of the class.

Each object increments the static count. After three objects, count is 3.

🧠 Conceptual

expert

Effect of const member function on data members

Which statement is true about const member functions in C++?

A They cannot access any data members of the class.

B They can modify any data member of the class.

C They can modify data members marked as mutable.

D They can only be called on non-const objects.

💡 Hint

Const member functions promise not to change the object except for mutable members.

Const member functions cannot modify normal data members but can modify those declared mutable.