IT INTERVIEW TIPS
C++
Interview Questions
A list of
top frequently asked C++ interview questions and answers are given below.
1) What is C++?
C++ is an
object-oriented programming language created by Bjarne Stroustrup. It was
released in 1985.
C++ is a
superset of C with the major addition of classes in C language.
Initially,
Stroustrup called the new language "C with classes". However, after
sometime the name was changed to C++. The idea of C++ comes from the C
increment operator ++.
2) What are the
advantages of C++?
C++
doesn't only maintains all aspects from C language, it also simplifies memory
management and adds several features like:
o
C++ is a highly portable language means that the software
developed using C++ language can run on any platform.
o
C++ is an object-oriented programming language which includes the
concepts such as classes, objects, inheritance, polymorphism, abstraction.
o
C++ has the concept of inheritance. Through inheritance, one can
eliminate the redundant code and can reuse the existing classes.
o
Data hiding helps the programmer to build secure programs so that
the program cannot be attacked by the invaders.
o
Message passing is a technique used for communication between the
objects.
o
C++ contains a rich function library.
3) What is the
difference between C and C++?
Following
are the differences between C and C++:
|
C |
C++ |
|
C
language was developed by Dennis Ritchie. |
C++
language was developed by Bjarne Stroustrup. |
|
C is a
structured programming language. |
C++
supports both structural and object-oriented programming language. |
|
C is a
subset of C++. |
C++ is
a superset of C. |
|
In C
language, data and functions are the free entities. |
In the
C++ language, both data and functions are encapsulated together in the form
of a project. |
|
C does
not support the data hiding. Therefore, the data can be used by the outside
world. |
C++
supports data hiding. Therefore, the data cannot be accessed by the outside
world. |
|
C
supports neither function nor operator overloading. |
C++
supports both function and operator overloading. |
|
In C,
the function cannot be implemented inside the structures. |
In the
C++, the function can be implemented inside the structures. |
|
Reference
variables are not supported in C language. |
C++
supports the reference variables. |
|
C language
does not support the virtual and friend functions. |
C++
supports both virtual and friend functions. |
|
In C,
scanf() and printf() are mainly used for input/output. |
C++
mainly uses stream cin and cout to perform input and output operations. |
4) What is the
difference between reference and pointer?
Following
are the differences between reference and pointer:
|
Reference |
Pointer |
|
Reference
behaves like an alias for an existing variable, i.e., it is a temporary
variable. |
The
pointer is a variable which stores the address of a variable. |
|
Reference
variable does not require any indirection operator to access the value. A
reference variable can be used directly to access the value. |
Pointer
variable requires an indirection operator to access the value of a variable. |
|
Once
the reference variable is assigned, then it cannot be reassigned with
different address values. |
The
pointer variable is an independent variable means that it can be reassigned
to point to different objects. |
|
A null
value cannot be assigned to the reference variable. |
A null
value can be assigned to the reference variable. |
|
It is
necessary to initialize the variable at the time of declaration. |
It is
not necessary to initialize the variable at the time of declaration. |
5) What is a class?
The class
is a user-defined data type. The class is declared with the keyword class. The
class contains the data members, and member functions whose access is defined
by the three modifiers are private, public and protected. The class defines the
type definition of the category of things. It defines a datatype, but it does
not define the data it just specifies the structure of data.
You can
create N number of objects from a class.
6)
What are the various OOPs concepts in C++?
The various OOPS concepts in C++ are:
o
Class:
The class is a user-defined data type which defines its
properties and its functions. For example, Human being is a class. The body
parts of a human being are its properties, and the actions performed by the
body parts are known as functions. The class does not occupy any memory space.
Therefore, we can say that the class is the only logical representation of the
data.
The syntax of declaring the class:
1. class student
2. {
3. //data members;
4. //Member functions
5. }
o
Object:
An object is a run-time entity. An object is the instance of
the class. An object can represent a person, place or any other item. An object
can operate on both data members and member functions. The class does not
occupy any memory space. When an object is created using a new keyword, then
space is allocated for the variable in a heap, and the starting address is
stored in the stack memory. When an object is created without a new keyword,
then space is not allocated in the heap memory, and the object contains the null
value in the stack.
1. class Student
2. {
3. //data members;
4. //Member functions
5. }
The syntax for declaring the object:
1. Student s = new Student();
o
Inheritance:
Inheritance provides reusability. Reusability means that one
can use the functionalities of the existing class. It eliminates the redundancy
of code. Inheritance is a technique of deriving a new class from the old class.
The old class is known as the base class, and the new class is known as derived
class.
Syntax
1. class derived_class :: visibility-mode base_class;
Note: The
visibility-mode can be public, private, protected.
o
Encapsulation:
Encapsulation is a technique of wrapping the data members and
member functions in a single unit. It binds the data within a class, and no
outside method can access the data. If the data member is private, then the
member function can only access the data.
o
Abstraction:
Abstraction is a technique of showing only essential details
without representing the implementation details. If the members are defined
with a public keyword, then the members are accessible outside also. If the
members are defined with a private keyword, then the members are not accessible
by the outside methods.
o
Data binding:
Data binding is a process of binding the application UI and
business logic. Any change made in the business logic will reflect directly to
the application UI.
o
Polymorphism:
Polymorphism means multiple forms. Polymorphism means having
more than one function with the same name but with different functionalities. Polymorphism
is of two types:
1. Static polymorphism is also known as early binding.
2. Dynamic polymorphism is also known as late binding.
7)
What are the different types of polymorphism in C++?
Polymorphism: Polymorphism means multiple forms. It means
having more than one function with the same function name but with different
functionalities.
Polymorphism is of two types:
o
Runtime polymorphism
Runtime polymorphism is also known as dynamic polymorphism.
Function overriding is an example of runtime polymorphism. Function overriding
means when the child class contains the method which is already present in the
parent class. Hence, the child class overrides the method of the parent class.
In case of function overriding, parent and child class both contains the same
function with the different definition. The call to the function is determined
at runtime is known as runtime polymorphism.
Let's understand this through an example:
1. #include <iostream>
2. using namespace std;
3. class Base
4. {
5. public:
6. virtual void show()
7. {
8. cout<<"javaTpoint";
9. }
10. };
11. class Derived:public Base
12. {
13. public:
14. void show()
15. {
16. cout<<"javaTpoint tutorial";
17. }
18. };
19.
20. int main()
21. {
22. Base* b;
23. Derived d;
24. b=&d;
25. b->show();
26. return 0;
27. }
Output:
javaTpoint
tutorial
o
Compile time
polymorphism
Compile-time polymorphism is also known as static
polymorphism. The polymorphism which is implemented at the compile time is
known as compile-time polymorphism. Method overloading is an example of
compile-time polymorphism.
Method overloading: Method overloading is a technique which allows you to
have more than one function with the same function name but with different
functionality.
Method overloading can be possible on the following basis:
o
The return type of the overloaded
function.
o
The type of the parameters passed to the
function.
o
The number of parameters passed to the
function.
Let's understand this through an example:
1. #include <iostream>
2. using namespace std;
3. class Multiply
4. {
5. public:
6. int mul(int a,int b)
7. {
8. return(a*b);
9. }
10. int mul(int a,int b,int c)
11. {
12. return(a*b*c);
13. }
14. };
15. int main()
16. {
17. Multiply multi;
18. int res1,res2;
19. res1=multi.mul(2,3);
20. res2=multi.mul(2,3,4);
21. cout<<"\n";
22. cout<<res1;
23. cout<<"\n";
24. cout<<res2;
25. return 0;
26. }
Output:
6
24
o
In the above example, mul() is an
overloaded function with the different number of parameters.
8)
Define namespace in C++.
o
The namespace is a logical division of the
code which is designed to stop the naming conflict.
o
The namespace defines the scope where the
identifiers such as variables, class, functions are declared.
o
The main purpose of using namespace in C++
is to remove the ambiguity. Ambiquity occurs when the different task occurs
with the same name.
o
For example: if there are two functions
exist with the same name such as add(). In order to prevent this ambiguity, the
namespace is used. Functions are declared in different namespaces.
o
C++ consists of a standard namespace,
i.e., std which contains inbuilt classes and functions. So, by using the
statement "using namespace std;" includes the namespace
"std" in our program.
o
Syntax of namespace:
1. namespace namespace_name
2. {
3. //body of namespace;
4. }
Syntax of accessing the namespace variable:
1. namespace_name::member_name;
Let's understand this through an example:
1. #include <iostream>
2. using namespace std;
3. namespace addition
4. {
5. int a=5;
6. int b=5;
7. int add()
8. {
9. return(a+b);
10. }
11. }
12.
13. int main() {
14. int result;
15. result=addition::add();
16. cout<<result;
17. return 0;
18. }
Output:
10
9)
Define token in C++.
A token in C++ can be a keyword, identifier, literal,
constant and symbol.
10)
Who was the creator of C++?
Bjarne Stroustrup.
11)
Which operations are permitted on pointers?
Following are the operations that can be performed on
pointers:
o
Incrementing or
decrementing a pointer:
Incrementing a pointer means that we can increment the pointer by the size of a
data type to which it points.
There are two types of increment pointers:
1. Pre-increment pointer: The pre-increment operator increments the operand by 1, and
the value of the expression becomes the resulting value of the incremented.
Suppose ptr is a pointer then pre-increment pointer is represented as ++ptr.
Let's understand this through an example:
1. #include <iostream>
2. using namespace std;
3. int main()
4. {
5. int a[5]={1,2,3,4,5};
6. int *ptr;
7. ptr=&a[0];
8. cout<<"Value of *ptr is : "<<*ptr<<"\n";
9. cout<<"Value of *++ptr : "<<*++ptr;
10. return 0;
11. }
Output:
Value
of *ptr is : 1
Value
of *++ptr : 2
2. Post-increment pointer: The post-increment operator increments the operand by 1,
but the value of the expression will be the value of the operand prior to the
incremented value of the operand. Suppose ptr is a pointer then post-increment
pointer is represented as ptr++.
Let's understand this through an example:
1. #include <iostream>
2. using namespace std;
3. int main()
4. {
5. int a[5]={1,2,3,4,5};
6. int *ptr;
7. ptr=&a[0];
8. cout<<"Value of *ptr is : "<<*ptr<<"\n";
9. cout<<"Value of *ptr++ : "<<*ptr++;
10. return 0;
11. }
Output:
Value
of *ptr is : 1
Value
of *ptr++ : 1
o
Subtracting a pointer
from another pointer: When
two pointers pointing to the members of an array are subtracted, then the
number of elements present between the two members are returned.
12)
Define 'std'.
Std is the default namespace standard used in C++.
13)
Which programming language's unsatisfactory performance led to the discovery of
C++?
C++was discovered in order to cope with the disadvantages of
C.
14)
How delete [] is different from delete?
Delete is used to release a unit of memory, delete[] is used
to release an array.
15)
What is the full form of STL in C++?
STL stands for Standard Template Library.
16)
What is an object?
The Object is the instance of a class. A class provides a
blueprint for objects. So you can create an object from a class. The objects of
a class are declared with the same sort of declaration that we declare
variables of basic types.
17)
What are the C++ access specifiers?
The access specifiers are used to define how to functions and
variables can be accessed outside the class.
There are three types of access specifiers:
o
Private: Functions and variables declared as private can be accessed
only within the same class, and they cannot be accessed outside the class they
are declared.
o
Public: Functions and variables declared under public can be
accessed from anywhere.
o
Protected: Functions and variables declared as protected cannot be
accessed outside the class except a child class. This specifier is generally
used in inheritance.
18)
What is Object Oriented Programming (OOP)?
OOP is a methodology or paradigm that provides many concepts.
The basic concepts of Object Oriented Programming are given below:
Classes and Objects: Classes are used to specify the structure of the data. They
define the data type. You can create any number of objects from a class.
Objects are the instances of classes.
Encapsulation:
Encapsulation is a mechanism which binds the data and associated operations
together and thus hides the data from the outside world. Encapsulation is also
known as data hiding. In C++, It is achieved using the access specifiers, i.e.,
public, private and protected.
Abstraction:
Abstraction is used to hide the internal implementations and show only the
necessary details to the outer world. Data abstraction is implemented using
interfaces and abstract classes in C++.
Some people confused about Encapsulation and abstraction, but
they both are different.
Inheritance:
Inheritance is used to inherit the property of one class into another class. It
facilitates you to define one class in term of another class.
19)
What is the difference between an array and a list?
o
An Array is a collection of homogeneous
elements while a list is a collection of heterogeneous elements.
o
Array memory allocation is static and
continuous while List memory allocation is dynamic and random.
o
In Array, users don't need to keep in
track of next memory allocation while In the list, the user has to keep in
track of next location where memory is allocated.
20)
What is the difference between new() and malloc()?
o
new() is a preprocessor while malloc() is
a function.
o
There is no need to allocate the memory
while using "new" but in malloc() you have to use sizeof().
o
"new" initializes the new memory
to 0 while malloc() gives random value in the newly allotted memory location.
o
The new() operator allocates the memory
and calls the constructor for the object initialization and malloc() function
allocates the memory but does not call the constructor for the object
initialization.
o
The new() operator is faster than the
malloc() function as operator is faster than the function.
21)
What are the methods of exporting a function from a DLL?
There are two ways:
o
By using the DLL's type library.
o
Taking a reference to the function from
the DLL instance.
22)
Define friend function.
Friend function acts as a friend of the class. It can access
the private and protected members of the class. The friend function is not a
member of the class, but it must be listed in the class definition. The
non-member function cannot access the private data of the class. Sometimes, it
is necessary for the non-member function to access the data. The friend
function is a non-member function and has the ability to access the private
data of the class.
To make an outside function friendly to the class, we need to
declare the function as a friend of the class as shown below:
1. class sample
2. {
3. // data members;
4. public:
5. friend void abc(void);
6. };
Following are the characteristics of a friend function:
o
The friend function is not in the scope of
the class in which it has been declared.
o
Since it is not in the scope of the class,
so it cannot be called by using the object of the class. Therefore, friend
function can be invoked like a normal function.
o
A friend function cannot access the
private members directly, it has to use an object name and dot operator with
each member name.
o
Friend function uses objects as arguments.
Let's understand this through an example:
1. #include <iostream>
2. using namespace std;
3. class Addition
4. {
5. int a=5;
6. int b=6;
7. public:
8. friend int add(Addition a1)
9. {
10. return(a1.a+a1.b);
11. }
12. };
13. int main()
14. {
15. int result;
16. Addition a1;
17. result=add(a1);
18. cout<<result;
19. return 0;
20. }
Output:
11
23)
What is a virtual function?
o
A virtual function is used to replace the
implementation provided by the base class. The replacement is always called
whenever the object in question is actually of the derived class, even if the object
is accessed by a base pointer rather than a derived pointer.
o
A virtual function is a member function
which is present in the base class and redefined by the derived class.
o
When we use the same function name in both
base and derived class, the function in base class is declared with a keyword
virtual.
o
When the function is made virtual, then
C++ determines at run-time which function is to be called based on the type of
the object pointed by the base class pointer. Thus, by making the base class pointer
to point different objects, we can execute different versions of the virtual
functions.
Rules of a virtual function:
o
The virtual functions should be a member
of some class.
o
The virtual function cannot be a static
member.
o
Virtual functions are called by using the
object pointer.
o
It can be a friend of another class.
o
C++ does not contain virtual constructors
but can have a virtual destructor.
24)
When should we use multiple inheritance?
You can answer this question in three manners:
1. Never
2. Rarely
3. If you find that the problem domain cannot be accurately
modeled any other way.
25)
What is a destructor?
A Destructor is used to delete any extra resources allocated
by the object. A destructor function is called automatically once the object
goes out of the scope.
Rules of destructor:
o
Destructors have the same name as class
name and it is preceded by tilde.
o
It does not contain any argument and no
return type.
26)
What is an overflow error?
It is a type of arithmetical error. It happens when the
result of an arithmetical operation been greater than the actual space provided
by the system.
27)
What is overloading?
o
When a single object behaves in many ways
is known as overloading. A single object has the same name, but it provides
different versions of the same function.
o
C++ facilitates you to specify more than
one definition for a function name or an operator in the same scope. It is
called function overloading and operator overloading respectively.
o
Overloading is of two
types:
1. Operator overloading: Operator overloading is a compile-time polymorphism in
which a standard operator is overloaded to provide a user-defined definition to
it. For example, '+' operator is overloaded to perform the addition operation
on data types such as int, float, etc.
Operator overloading can be implemented in the following
functions:
o
Member function
o
Non-member function
o
Friend function
Syntax of Operator overloading:
1. Return_type classname :: Operator Operator_symbol(argument_list)
2. {
3. // body_statements;
4. }
2. Function overloading: Function overloading is also a type of compile-time
polymorphism which can define a family of functions with the same name. The
function would perform different operations based on the argument list in the
function call. The function to be invoked depends on the number of arguments
and the type of the arguments in the argument list.
28)
What is function overriding?
If you inherit a class into a derived class and provide a
definition for one of the base class's function again inside the derived class,
then this function is called overridden function, and this mechanism is known
as function overriding.
29)
What is virtual inheritance?
Virtual inheritance facilitates you to create only one copy
of each object even if the object appears more than one in the hierarchy.
30)
What is a constructor?
A Constructor is a special method that initializes an object.
Its name must be same as class name.
31)
What is the purpose of the "delete" operator?
The "delete" operator is used to release the
dynamic memory created by "new" operator.
32)
Explain this pointer?
This pointer holds the address of the current object.
33)
What does Scope Resolution operator do?
A scope resolution operator(::) is used to define the member
function outside the class.
34)
What is the difference between delete and delete[]?
Delete [] is used to release the array of allocated memory
which was allocated using new[] whereas delete is used to release one chunk of
memory which was allocated using new.
35)
What is a pure virtual function?
The pure virtual function is a virtual function which does
not contain any definition. The normal function is preceded with a keyword
virtual. The pure virtual function ends with 0.
Syntax of a pure virtual function:
1. virtual void abc()=0; //pure virtual function.
Let's understand this through an example:
1. #include<iostream>
2. using namespace std;
3. class Base
4. {
5. public:
6. virtual void show()=0;
7. };
8.
9. class Derived:public Base
10. {
11. public:
12. void show()
13. {
14. cout<<"javaTpoint";
15. }
16. };
17. int main()
18. {
19. Base* b;
20. Derived d;
21. b=&d;
22. b->show();
23. return 0;
24. }
Output:
javaTpoint
36)
What is the difference between struct and class?
|
Structures |
class |
|
A structure
is a user-defined data type which contains variables of dissimilar data
types. |
The
class is a user-defined data type which contains member variables and member
functions. |
|
The
variables of a structure are stored in the stack memory. |
The
variables of a class are stored in the heap memory. |
|
We
cannot initialize the variables directly. |
We can
initialize the member variables directly. |
|
If
access specifier is not specified, then by default the access specifier of
the variable is "public". |
If
access specifier is not specified, then by default the access specifier of a
variable is "private". |
|
The
instance of a structure is a "structure variable". |
|
|
Declaration
of a structure: struct structure_name { //
body of structure; } ; |
Declaration
of class: class class_name { //
body of class; } |
|
A
structure is declared by using a struct keyword. |
The
class is declared by using a class keyword. |
|
The
structure does not support the inheritance. |
The
class supports the concept of inheritance. |
|
The
type of a structure is a value type. |
The
type of a class is a reference type. |
37)
What is a class template?
A class template is used to create a family of classes and
functions. For example, we can create a template of an array class which will
enable us to create an array of various types such as int, float, char, etc.
Similarly, we can create a template for a function, suppose we have a function
add(), then we can create multiple versions of add().
The syntax of a class template:
1. template<class T>
2. class classname
3. {
4. // body of class;
5. };
Syntax of a object of a template class:
1. classname<type> objectname(arglist);
38)
What is the difference between function overloading and operator overloading?
Function overloading: Function overloading is defined as we can have more
than one version of the same function. The versions of a function will have
different signature means that they have a different set of parameters.
Operator overloading: Operator overloading is defined as the standard
operator can be redefined so that it has a different meaning when applied to
the instances of a class.
39)
What is a virtual destructor?
A virtual destructor in C++ is used in the base class so that
the derived class object can also be destroyed. A virtual destructor is
declared by using the ~ tilde operator and then virtual keyword before the
constructor.
Note: Constructor cannot
be virtual, but destructor can be virtual.
Let's understand this through an example
o
Example without using virtual destructor
1. #include <iostream>
2. using namespace std;
3. class Base
4. {
5. public:
6. Base()
7. {
8. cout<<"Base constructor is called"<<"\n";
9. }
10. ~Base()
11. {
12. cout<<"Base class object is destroyed"<<"\n";
13. }
14. };
15. class Derived:public Base
16. {
17. public:
18. Derived()
19. {
20. cout<<"Derived class constructor is called"<<"\n";
21. }
22. ~Derived()
23. {
24. cout<<"Derived class object is destroyed"<<"\n";
25. }
26. };
27. int main()
28. {
29. Base* b= new Derived;
30. delete b;
31. return 0;
32.
33. }
Output:
Base
constructor is called
Derived
class constructor is called
Base
class object is destroyed
In the above example, delete b will only call the base class
destructor due to which derived class destructor remains undestroyed. This
leads to the memory leak.
o
Example with a virtual destructor
1. #include <iostream>
2. using namespace std;
3. class Base
4. {
5. public:
6. Base()
7. {
8. cout<<"Base constructor is called"<<"\n";
9. }
10. virtual ~Base()
11. {
12. cout<<"Base class object is destroyed"<<"\n";
13. }
14. };
15. class Derived:public Base
16. {
17. public:
18. Derived()
19. {
20. cout<<"Derived class constructor is called"<<"\n";
21. }
22. ~Derived()
23. {
24. cout<<"Derived class object is destroyed"<<"\n";
25. }
26. };
27. int main()
28. {
29. Base* b= new Derived;
30. delete b;
31. return 0;
32.
33. }
Output:
Base
constructor is called
Derived
class constructor is called
Derived
class object is destroyed
Base
class object is destroyed
When we use the virtual destructor, then the derived class
destructor is called first, and then the base class destructor is called.
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