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C++ Technical Questions

These are the C++ Basic Fundamental Questions asked in Interviews or Vivas.

1.       What is the difference between oop and pop?
A.       Pop consists of writing a list of instructions for the computer to follow and originating these instructions into groups known as functions. Oops treats data as a critical element  in the pgm development and does not allow it to flow forcely around the system. It protects data from accidental modification which is from outside functions.

2.       What is a class and object?
A.       The objects contains the data and the code to manipulate that data. So, the entire set of data and code of an object can be made a user defined datatype with the help of classes.
Objects are basic run timeentities in an object oriented system.they may  represent a person, a place, a bank a/c or any data item that pgm has to handle.

3.       What is meant by encapsulation?
A.      The method of combining the data and functions into single unit is called as data encapsulation.

4.       What is polymorphism?
A.       It is the ability to take morethan oneform i.e., an operation may exhibit different behaviours in different instances. there are two types. they are:
Static : the functions that are known at compilation time.
Dynamic: the functions that are known at execution time.

5.       What are different access specifiers and difference between them?
A.      The members which has been declared as private are accessible only with in class and the member functions of that class.
The members that have been declared as public can be accessed outside of the class also.
The members which are declared as protected can be accessed in the class or immediate derived class.

6.       What is meant by function overloading?
A.      Overloading means the use of the same thing or same function for different purposes. C++ allows  overloading of different functions i.e., we can use the same function to perform different tasks with same function name. this is also called as function polymorphism.

7.       What is cout and cin?
A.      COUT: it is  the o/p statement is used to display the values of  variables on the screen or moniter.
CIN: it is a predefined object in c++ that represents standard i/p stream.

8.       What is void pointer?
A.      To specify the return type of a function when it is not returning any value.
To indicate an empty argument list to a function.
In c++ void is used as generic pointer.

9.       What is reference variable?
A.      C++ includes a new kind of variables known as reference variable. A reference variables provides an alias name for a previously defined variables.
Format: datatype &reference variable=variable;

10.    Define size-t?
A.      It is one of the variable like int or char. It is used in new operator overloading concept.

11.    Difference between reference & pointer variable?
A.       In reference we shall access the duplicate af the variables by aliasing them.
In pointer we shall access the variables using their addresses.

12.    What is the difference between constant pointer and pointer to a constant?
A.      Constant pointer: const *p=10;
Pointer to a constant: const a=10;

13.    What is dazzling pointer?
A.       The pointer that points to a block of memory that does not exist is called a dazzling pointer or wild pointer.

14.    What is the difference between classes and structures in c++?
A.      Classes: in classes there is a security for variables.
Structures: in this there is no security for data members and variables.

15.    What is the importance of scope resolution operator?
A.      It is used for the purpose of accessing a total variable name with in the function, when the global variable and local variable have the same name. It is used to uncover a hidden variable.

16.    What is the scope and life time?
A.      Scope: scope is  defined in which the variables defined.
Life time: it is defined as the ----- position in which the variable is defined.

17.    What is the importance of static data member?
A.      In some situations it is necessary to store the data members for the all objects, so we use static data member.

18.    What are the main characteristics of static member functions?
A.      A static function can have access to only static data members declared in the same class.
              Classname:: function name(arguments);

19.    What is a friend function?
A.      The friend function can be declared by using the resolved word friend. The functions that are declared with the keyword friend is known as friend function.

20.    What is the importance of friend function?
A.       It can be declared either a public or private part of the class without effecting its meaning.
It can’t be called using the ojects of the class and it can be invoked like a normal function.

21.   What is a friend class?
A.       We can also declare all the member functions of one class as the friend functions of another class. This class is friend class.

22.   What are the disadvantages of friend function?
A.      We can overload some operators.
It violates the datahiding concept by accessing private data members.

23.   What is meant by Ambiguity?
A.      In Function overloading,some times functions are created with one function name,same argument list and same return type.This time the ambiguity occurs.

24.   Write the syntax for declaration of reference variable?
A.      Datatype &reference variable=variable;

25.   What is an Inline function?
A.      An inline function is a function that is expanded in a line when it is invoked.
            Inline datatype functionname(arguments list){ }

26.   What is the rule to initialize the default arguments?
A.       C++ allows us to call a function without specifying all its arguments.In such cases,the function assigns a default value to the parameter which does not have a matching argument in the function call.Default values are specified when the function is declared.
Float amount(float principal,int period,float rate=0.15);
The subsequent function call is

27.   What is the importance of constant arguments?
A.      Int strlen(const char *p);
        The qualifier const tells the compiler that the function should not modify the argument.The compiler wouldn’t allow to modify the argument.This type of declaration is significant only when we pass arguments by reference or pointers.

28.   What is constructor and destructor? What is the importance of constructor?
A.      A constructor is a special member function whose task is to initialize the objects of its class.
Importance:It is special because its name is the same as the class name.When an object is created ,the constructor is invoked.
It is called constructor because it constructs the values of data members of the class.

       A destructor is used to destroy the objects that have been created by a constructor.Like a constructor ,the destructor is a member function whose name is the same as the class name but is preceded by a tilde(~).
Ex:~integer( ) { }

29.   Can we overload the destructor ?
A.      No,we can’t overload the destructor because it destroys the object.

30.   Write the syntax to define the copy constructor?
A.      A copy constructor is used to declare and initialize an object with the contents of another object.
         Classname obj2=obj1;
         Classname obj2(obj1);

31.   What is implicit constructor supplied by compiler?
A.      A constructor can also have default arguments which will be specified at the last arguments position in the argument list.whenever an object contains les number of arguments then the default arguments will be substituted.

32.   What is the syntax for defining constructor and destructor?
A.      Constructor:
         Class <classname>

33.   Write syntax for implicit and explicit calling of constructors?
A.      Implicit call:
                   <classname> <objectname>(list of values);
       Explicit call:
                   <classname> <objectname>=constructor(list of values);

34.   What is meant by operator overloading?
A.      The process of making an operator to exhibit different behaviours at different instances is known as Operator Overloading.

35.   List the operators which can’t be overloaded?
A.      Operator                             Meaning
    ::                         Scope resolution operator
    Sizeof( )                 Size of operator
    ?:                            Conditional or ternary operator
     .*                            Pointer to member access

36.   List the operators which can’t be overloaded using friend functions?
A.      Operator                           Meaning
    =                            Assignment operator
    ( )                           Function call operator
     [ ]                          Subscript operator
     ->                          Class member access operator

37.   What are the rules to overload unary and binary operators?
A.      Unary operators are overloaded bymeans of member functions takes no arguments and no return values and the unary operator can be overloaded by means of friend function which takes one reference argument.

Binary operator is overloaded through a member function which takes only one argument but the binary argument is overloaded through a friend function takes two explicit arguments.

38.   Write the syntax to overload unary and binary operator?
A.      Returntype operator operatorname(  )


Friend returntype operator operatorname(classname &address)


39.   What is an operator function?
A.      In case of conversion from user defined to basic type the conversion function should be defined in
User defined class in the form of operator function.

40.   What is the syntax for operator function?
A.      Operator basicdatatype(  )


41.   How to differentiate post and preincrement operator overloading?
A.      Prefix:
Returntype operator ++( );
Returntype classname::operator ++( )


Returntype operator ++(int x);
Returntype classname::operator ++( int x)


42.   Can you declare a destructor as static?
A.      No,we can’t declare a destructor as static because suppose when we declare a destructor as static the class will be destroyed.

43.   What is meant by Inheritance?
A.      The process by which objects of one class acquire the properties of another class is called inheritance.

44.   How can you inherit private members?
A.      This can be accomplished by modifying the visibility limit of the private member by making it as public.

45.   What are different visibility modes in Inheritance?
A.      There are three modes.

46.   How the constructors and destructors are moved in case of multiple inheritance?
A.      In case of multiple inheritance the base classes are constructed in the order in which they appear in the derived class.The base constructors are called and executed before executing the statements in the body of the derived constructor.

47.   Write the syntax to initialize base class constructor?
A.      Derived constructor (a1,a2,a3):base1constructor(a1),base2constructor(a2)


48.   What is virtual base class?
A.      To eliminate duplicate copies C++ allows a technique called virtual baseclass.Here only one copy of base class is copied.

49.   What is the difference between Function overloading and function over riding?
A.      The mechanism of deriving a function in the derived class for its own implementation which is already defined in the base class is called overriding.

Overloading                                                           Overriding
->The prototype of two functions are different      ->The prototype of two functions are same
->The names of the two functions are same       ->The names of the two functions are same

50.   How can you implement runtime polymorphism?
A.      It is implemented by using virtual functions.

51.   What is virtual function?
A.      The problem with the pointers to the derived class is that we cant access the public members of the derived class using pointers to the base class. We can access only those members which are inherited from the base class and not the members that originally belongs to the derived class.for a solution to the problem we have to use virtual functions.

52.   What is pure virtual function and write syntax for this?
A.      A pure virtual function is a function that has no definition with in the base class. When a base class member function is defined as empty such a function is called do nothing functions.
          Virtual returntype functionname(Arguments )=0;

53.   What is abstract class?
A.      An abstract class is one that is not used to create objects.An abstract class is designed only to act as a base class.the abstract base classes are generally used in inheritance.

54.   What is the use of abstract class?
A.      The main purpose of the abstract class is to derive a class from an already existing base class.

55.   What is Abstract datatype?
A.      Abstract collection of data elements and their accessing functions where we are not concerned about how the accessing function will be implemented is referred to as Abstract datatype.

56.   What is THIS pointer?
A.      This pointer is used to represent an object that invokes a member function.

57.   What is a file?
A.      A file is a collection of related data stored in a particular area on the disk.

58.   What is a Stream?
A.      The interface between the programmer and the I/O device is known as stream.A stream is a sequence of bytes.

59.   What are predefined stream classes?
A.      There are two types:
Istream and ostream

60.   What are standard streams?
A.      Cin : 
           It represents the input stream connected to standard input devices.
           It represents the output stream connected to standard output devices.
61.   What are formatted I/O operations?
A.      C++ supports a number of features which were used for formatting the output. They are
1.IOS class functions and flags
3.User defined manipulators.

62.   What are predefined functions in Input and output streams?
A.      Cin ,cout are the predefined functions in input and output streams.These are obtained automatically when a program begins its execution.

63.   Write formatting flags defined in the IOS class?
A.      IOS::adjust field
IOS::float field
IOS::base field

64.   What is the significance of bit field?
A.      These are used to justify and scientific notation of floating values.

65.   How to display trailing decimal points and zeros?
A.      Using IOS::show point ,here we can display trailing decimal points and zeros.

66.   What is a Manipulator?
A.      Manipulators are operators that are used to format the data display.The most commonly used manipulators are endl and setw.

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