C++ Programming Questions and Answers – Abstract Classes – 2

C++ Programming Multiple Choice Questions & Answers (MCQs) focuses on “Abstract Classes – 2”.

Q 1. What is an abstract class in C++?
A. Class specifically used as a base class with at least one virtual functions
B. Class specifically used as a base class with at least one pure virtual functions
C. Class from which any class is derived
D. Any Class in C++ is an abstract class

Show Answer

Answer:-B. Class specifically used as a base class with at least one pure virtual functions

Explanation

An abstract class is defined as a class which is specifically used as a base class. An abstract class should have atleast one pure virtual function.

Q 2. What is a pure virtual function in C++?
A. A virtual function defined in a base class
B. Any function in a class
C. A virtual function declared in a base class
D. A function without definition in a base class

Show Answer

Answer:-C. A virtual function declared in a base class

Explanation

Pure virtual function is a virtual function which has no definition/implementation in the base class.

Q 3. Which is the correct syntax of defining a pure virtual function?
A. virtual return_type func() = 0;
B. virtual return_type func() pure;
C. pure virtual return_type func();
D. virtual return_type func();

Show Answer

Answer:-A. virtual return_type func() = 0;

Explanation

virtual return_type function_name(parameters) = 0; where {=0} is called pure specifier. advertisement

Q 4. Which is the correct statement about pure virtual functions?
A. They should be defined inside a base class
B. Pure virtual function is implemented in derived classes
C. Pure keyword should be used to declare a pure virtual function
D. Pure virtual function cannot implemented in derived classes

Show Answer

Answer:-B. Pure virtual function is implemented in derived classes

Explanation

A pure virtual function does not have a definition corresponding to base class. All derived class may or may not have an implementation of a pure virtual function. there is no pure keyword in C++.

Q 5. Pick the correct statement.
A. Pure virtual functions and virtual functions are the same
B. Both Pure virtual function and virtual function have an implementation in the base class
C. Pure virtual function has no implementation in the base class whereas virtual function may have an implementation in the base class
D. The base class has no pure virtual function

Show Answer

Answer:-C. Pure virtual function has no implementation in the base class whereas virtual function may have an implementation in the base class

Explanation

Pure virtual function has no implementation in the base class whereas virtual function may have an implementation in the base class. The base class has at least one pure virtual function.

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

#include

using namespace std;

class A
{
int a; // This remains uninitialized, which is not a problem but can be explicitly initialized in a constructor
public:
virtual void func() = 0; // Pure virtual function
};

class B : public A
{
public:
void func() override {
cout << “Class B” << endl;
}
};

int main()
{
B b;
b.func(); // Calls the overridden function in class B
return 0;
}
A. Segmentation fault
B. Class B
C. Error
D. No output

Show Answer

Answer:-B. Class B

Explanation

The program is correct so no error occurs hence the program runs successfully and b is calling is func() function therefore “Class B” is printed.

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

#include

#include

using namespace std;
class A
{
int a;
public:
virtual void func() = 0;
};

class B: public A
{
public:
void func(){
cout<<“Class B”<<endl;
}
};

int main(int argc, char const *argv[])
{
A a;
a.func();
return 0;
}
A. Class B
B. No output
C. Segmentation fault
D. Error

Show Answer

Answer:-D. Error

Explanation

The C++ does allows to declare a normal object for an abstract class therefore the program throws an error as we are trying to declare an object of abstract class.

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

#include

#include

using namespace std;
class A
{
int a;
public:
virtual void func() = 0;
};

class B: public A
{
public:
void func(){
cout<<“Class B”<<endl;
}
};

int main(int argc, char const *argv[])
{
A *a;
a->func();
return 0;
}
A. Class B
B. Error
C. No output
D. Segmentation fault

Show Answer

Answer:-D. Segmentation fault

Explanation

As we are allowed to declare a pointer object of an abstract so the program does not give any compilation error but as there is no definition of func() function corresponding to class A, therefore, the program gives segmentation fault as it is not able to call such function from class A.