C++ Classes and Objects: Predict Output

C++ Classes and Objects

Predict Output Questions

1. Constructor Initialization

#include <iostream>

using namespace std;

class Test {

    int x;

public:

    Test(int a) {

        x = a;

    }

    void display() {

        cout << x;

    }

};

int main() {

    Test obj(10);

    obj.display();

    return 0;

}

Answer:

10

Explanation:

• Constructor assigns x = 10. The display() function prints the value of x.

2. Default Constructor

#include <iostream>

using namespace std;

class Demo {

    int x;

public:

    Demo() {

        x = 5;

    }

    void show() {

        cout << x;

    }

};

int main() {

    Demo d1;

    d1.show();

    return 0;

}

Answer:

5

Explanation:

Default constructor automatically sets x = 5 when object d1 is created.

3. Multiple Objects

#include <iostream>

using namespace std;

class Sample {

    int x;

public:

    Sample(int a) {

        x = a;

    }

    void display() {

        cout << x << " ";

    }

};

int main() {

    Sample s1(2), s2(4);

    s1.display();

    s2.display();

    return 0;

}

Answer:

2 4

Explanation:

• Two objects are created with different values. Each object stores its own copy of x.

4. Static Data Member

#include <iostream>

using namespace std;

class Count {

    static int x;

public:

    Count() {

        x++;

    }

    static void show() {

        cout << x;

    }

};

int Count::x = 0;

int main() {

    Count c1, c2, c3;

    Count::show();

    return 0;

}

Answer:

3

Explanation:

• x is static; hence shared among all objects.
• Each constructor call increments x. Three objects; hence x = 3.

5. Function Returning Object

#include <iostream>

using namespace std;

class Test {

    int x;

public:

    Test(int a) {

        x = a;

    }

    Test add(Test t) {

        return Test(x + t.x);

    }

    void display() {

        cout << x;

    }

};

int main() {

    Test t1(5), t2(7);

    Test t3 = t1.add(t2);

    t3.display();

    return 0;

}

Answer:

12

Explanation:

• t1.x = 5, t2.x = 7
• New object created with value 5 + 7 = 12.

6. Constructor Called Multiple Times

#include <iostream>

using namespace std;

class Demo {

public:

    Demo() {

        cout << "C ";

    }

};

int main() {

    Demo d1, d2;

    return 0;

}

Answer:

C C

Explanation:

• Constructor runs once per object. Two objects → prints twice.

7. Private Data Access

#include <iostream>

using namespace std;

class Test {

    int x;

public:

    void set(int a) {

        x = a;

    }

    void show() {

        cout << x;

    }

};

int main() {

    Test t;

    t.set(15);

    t.show();

    return 0;

}

Answer:

15

Explanation:

• Private variable x is accessed using public member function set().

8. Object as Function Argument

#include <iostream>

using namespace std;

class Sample {

    int x;

public:

    Sample(int a) { x = a; }

    void add(Sample s) {

        cout << x + s.x;

    }

};

int main() {

    Sample s1(3), s2(6);

    s1.add(s2);

    return 0;

}

Answer:

9

Explanation: s1.x = 3, s2.x = 6 → prints 3 + 6 = 9.

9. Copy Constructor (Default)

#include <iostream>

using namespace std;

class Test {

    int x;

public:

    Test(int a) { x = a; }

    void show() { cout << x; }

};

int main() {

    Test t1(8);

    Test t2 = t1;

    t2.show();

    return 0;

}

Answer:

8

Explanation: Default copy constructor copies the value of x from t1 to t2.

10. Destructor Execution Order

#include <iostream>

using namespace std;

class Demo {

public:

    ~Demo() {

        cout << "D ";

    }

};

int main() {

    Demo d1, d2;

    return 0;

}

Answer:

D D

Explanation:

• Destructor is called automatically when objects go out of scope (reverse order of creation).
• Two objects → destructor runs twice.

< Back to C++ Home Page >

* * * * *