C++ Programming Questions and Answers - Derived Classes

This section on C++ programming questions and answers focuses on “Derived Classes”. One shall practice these questions to improve their C++ programming skills needed for various interviews (campus interviews, walkin interviews, company interviews), placements, entrance exams and other competitive exams. These questions can be attempted by anyone focusing on learning C++ programming language. They can be a beginner, fresher, engineering graduate or an experienced IT professional. Our C++ programming questions come with detailed explanation of the answers which helps in better understanding of C++ concepts.

Here is a listing of C++ programming questions on “Derived Classes” along with answers, explanations and/or solutions:

1. Where is the derived class is derived from?
a) derived
b) base
c) both derived & base
d) class
View Answer

Answer: b
Explanation: Because derived inherits functions and variables from base.

2. Pick out the correct statement.
a) A derived class’s constructor cannot explicitly invokes its base class’s constructor
b) A derived class’s destructor cannot invoke its base class’s destructor
c) A derived class’s destructor can invoke its base class’s destructor
d) A derived class’s destructor can invoke its base & derived class’s destructor
View Answer

Answer: b
Explanation: Destructors are automatically invoked when an object goes out of scope or when a dynamically allocated object is deleted. Inheritance does not change this behavior. This is the reason a derived destructor cannot invoke its base class destructor.

3. Which of the following can derived class inherit?
a) members
b) functions
c) both members & functions
d) classes
View Answer

Answer: c
Explanation: Both data members and member functions are inherited by derived class in C++.

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

```
    #include <iostream>
```
```
    using namespace std;
```
```
    class A
```
```
    {
```
```
        public:
```
```
        A(int n )
```
```
        {
```
```
            cout << n;
```
```
        }
```
```
    };
```
```
    class B: public A
```
```
    {
```
```
        public:
```
```
        B(int n, double d)
```
```
        : A(n)
```
```
        {
```
```
            cout << d;
```
```
        }    
```
```
    };
```
```
    class C: public B
```
```
    {
```
```
        public:
```
```
        C(int n, double d, char ch)
```
```
        : B(n, d)
```
```
        {
```
```
            cout <<ch;
```
```
        }
```
```
    };
```
```
    int main()
```
```
    {
```
```
        C c(5, 4.3, 'R');
```
```
        return 0;
```
```
    }
```

a) 54.3R
b) R4.35
c) 4.3R5
d) R2.6
View Answer

Answer: a
Explanation: In this program, We are passing the value and manipulating by using the derived class.
Output:

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$ g++ der.cpp
$ a.out
54.3R

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

```
    #include <iostream>
```
```
    using namespace std;
```
```
    class BaseClass 
```
```
    {
```
```
        protected:
```
```
        int i;
```
```
        public:
```
```
        BaseClass(int x) 
```
```
        {
```
```
            i = x;
```
```
        }
```
```
        ~BaseClass() 
```
```
        {
```
```
        }
```
```
    };
```

    class DerivedClass: public BaseClass

```
    {
```
```
        int j;
```
```
        public:
```

        DerivedClass(int x, int y): BaseClass(y)

```
        {
```
```
            j = x;
```
```
        }
```
```
        ~DerivedClass() 
```
```
        {
```
```
        }
```
```
        void show() 
```
```
        {
```

            cout << i << " " << j << endl;

```
        }
```
```
    };
```
```
    int main()
```
```
    {
```
```
        DerivedClass ob(3, 4);
```
```
        ob.show();
```
```
        return 0;
```
```
    }
```

a) 3 4
b) 4 3
c) 4
d) 3
View Answer

Answer: b
Explanation: In this program, We are passing the values and assigning it to i and j and we are printing it.
Output:

$ g++ der1.cpp
$ a.out
4 3

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

```
    #include <iostream>
```
```
    using namespace std;
```
```
    class Base
```
```
    {
```
```
        public:
```
```
        int m;
```
```
        Base(int n=0)
```
```
        : m(n)
```
```
        {
```
```
            cout << "Base" << endl;
```
```
        }
```
```
    };
```
```
    class Derived: public Base
```
```
    {
```
```
        public:
```
```
        double d;
```
```
        Derived(double de = 0.0)
```
```
        : d(de)
```
```
        {
```
```
            cout << "Derived" << endl;
```
```
        }
```
```
    };
```
```
    int main()
```
```
    {
```

        cout << "Instantiating Base" << endl;

```
        Base cBase;
```

        cout << "Instantiating Derived" << endl;

```
        Derived cDerived;
```
```
        return 0;
```
```
    }
```

   Instantiating Base
   Base
   Instantiating Derived
   Base
   Derived

   Instantiating Base
   Instantiating Derived
   Base 
   Derived

   Instantiating Base
   Base
   Instantiating Derived
   Base

d) Instantiating Base
View Answer

Answer: a
Explanation: In this program, We are printing the execution order of the program.
Output:

$ g++ der2.cpp
$ a.out
Instantiating Base
Base
Instantiating Derived
Base
Derived

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

```
    #include <iostream>
```
```
    using namespace std;
```
```
    class Parent
```
```
    {
```
```
        public:
```
```
        Parent (void) 
```
```
        {     
```
```
            cout << "Parent()\n";
```
```
        }
```
```
        Parent (int i) 
```
```
        { 
```

            cout << "Parent("<< i << ")\n";

```
        };
```
```
        Parent (void) 
```
```
        { 
```
```
            cout << "~Parent()\n";
```
```
        }; 
```
```
    };
```
```
    class Child1 : public Parent { };
```
```
    class Child2 : public Parent
```
```
    {
```
```
        public:
```
```
        Child2 (void) 
```
```
        {
```
```
            cout << "Child2()\n";
```
```
        }
```
```
        Child2 (int i) : Parent (i) 
```
```
        {
```

            cout << "Child2(" << i << ")\n";

```
        }
```
```
        ~Child2 (void) 
```
```
        {
```
```
            cout << "~Child2()\n"; 
```
```
        }
```
```
    };
```
```
    int main (void)
```
```
    {
```
```
        Child1 a;
```
```
        Child2 b;
```
```
        Child2 c(42);
```
```
        return 0;
```
```
    }
```

   Parent()
   Parent()
   Child2()
   Parent(42)
   Child2(42)
   ~Child2()
   ~Parent()
   ~Child2()
   ~Parent()
   ~Parent()

b) error
c) runtime error
d) Parent(42)
View Answer

Answer: b
Explanation: In this program, We got an error in overloading because we didn’t invoke the destructor of parent.

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

```
    #include<iostream>
```
```
    using namespace std;
```
```
    class X 
```
```
    {
```
```
        int m;
```
```
        public:
```
```
        X() : m(10)
```

```
        }
```
```
        X(int mm): m(mm)
```
```
        {
```
```
        }
```
```
        int getm()
```
```
        {
```
```
            return m;
```
```
        }
```
```
    };
```
```
    class Y : public X 
```
```
    {
```
```
        int n;
```
```
        public:
```

        Y(int nn) : n(nn) {}

```
        int getn() { return n; }
```
```
    };
```
```
    int main()
```
```
    {
```
```
        Y yobj( 100 );
```

        cout << yobj.getm() << " " << yobj.getn() << endl;

```
    }
```

a) 10 100
b) 100 10
c) 10 10
d) 100 100
View Answer

Answer: a
Explanation: In this program, We are passing the value and getting the result by derived class.
Output:

$ g++ der5.cpp
$ a.out
10 100

9. Which operator is used to declare the destructor?
a) #
b) ~
c) @
d) $
View Answer

Answer: b
Explanation: tilde(~) is used to declare destructor of a class.

10. Which constructor will initialize the base class data member?
a) derived class
b) base class
c) class
d) derived & base class
View Answer

Answer: b
Explanation: Because it is having the proper data set to initialize, Otherwise it will throw an error.

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