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Define Friend classes. What are advantages of using friend classes?

The friend function is a ‘non member function’ of a class. It can access non public members of the class. A friend function is external to the class definition.

A friend function has the following advantages:

- Provides additional functionality which is kept outside the class.
- Provides functions that need data which is not normally used by the class.
- Allows sharing private class information by a non member function.

What are zombie objects in C++. Explain its purpose.

An object creation of a class is failed before executing its constructor. As a constructor would not return a value, there is no confirmation that whether the constructor is executed completely or not.

An object that is freed does not crash the applications. The application debugging is allowed by making the all states of the object intact.

When are memory leaks important? What are the easiest ways to avoid memory leak?

Memory Leaks:

Memory leaks take up more memory space and causes slow calculation.
Ensure that the loops or conditional statements are executed completely to prevent memory leak occurrence.

The best and easiest way to avoid memory leaks is to make changes at the time of writing programs. The cause for this is, a properly planned program can avoid memory leaks. In addition to it, make a code snippet can be made simple, small which executes fast.

Explain the difference between Stack and Queue.

Stack is a Last in First out (LIFO) data structure whereas Queue is a First in First out (FIFO) data structure.

What is Stacks? Explain its uses.

Stack is a Last in First out (LIFO) data structure. It is a linear structure and one can insert and delete from one end only which is called the top. It is very effective in rectifying syntax errors like missing parentheses etc.

What is pure virtual function?

A pure virtual function is one which is initialized with 0 at the time of declaration.

What is a Wrapper class?

Wrapper classes are classes that allow primitive types to be accessed as objects.

What do you mean by Stack unwinding?

When an exception is thrown, C++ calls destructors to destroy all the objects formed since the beginning of the try block. The objects are destroyed in the reverse order of their formation. This process is called Stack unwinding.

What is the use of ‘using’ declaration?

In using-declaration, we have using keyword followed by a fully qualified name of a namespace member. This allows using the non-qualified name of that member in the scope of the using-declaration.

What is the difference between Mutex and Binary semaphore?

Semaphore synchronizes processes where as mutex synchronizes threads running in the same process.

What is the scope resolution operator?

Scope resolution operator allows a program to reference an identifier in the global scope that is hidden by another identifier with the same name in the local scope.

What is abstraction?

It is the process of hiding unwanted details from the user.

What are the advantages of inheritance?

Code reusability
Saves time in program development.

What is a conversion constructor?

It is a constructor that accepts one argument of a different type.

What is a default constructor?

A constructor that has no argument is a default constructor.

Explain the advantages if inline functions.

It relieves the burden involved in calling a function. It is used for functions that need fast execution.

Explain the different access specifiers for the class member in C++.

private: It is default one and can be access from class member of the same class.
protected: The protected members can be access from member functions of the same class or friend classes or from the members of their immediate derived class.
public: The public members can be access from anywhere the class is visible.

What is the importance of mutable keyword?

The mutable keyword allows the data member of a class to change within a const member function.

Pointer vs. reference.

A reference must be initialized at the time of declaration whereas not needed in case of pointer. A pointer can point to a null object.

A reference once initialize to refer to the object can't be reassigned to refer to other whereas reassignment is possible with pointer.

Explain how to call C functions from C++.

The extern keyword is used to call C functions from C++

extern "C" void showme()

What is static member?

A static member is created and initialize once and shared among all class objects.

Explain static member functions.

The static member functions are created to access static variables of a class.

How do we declare a class as a friend of another class?

class a
{
friend class b; // with this declaration, class b can access all members of a
};

Explain the private, protected and public inheritance.

private inheritance: all the public and protected members in base become private.
protected inheritance: all the public and protected members in base class become protected.
public inheritance: in case of public inheritance, public remains public and protected remains protected.

Class vs. Structure

Class

Class has private as default access specifier.
Default inheritance type is private.

Structure

Structure has public as default access specifier
Default inheritance type is public.

Explain with an example how to call a base member function from derived class member function.

class emp
{
public:
void empName()
{
cout << "emp-XYZ" <<>

Output

dept-XYZ
emp-XYZ

Is it possible to overload a constructor?

Yes it is possible. A constructor can be overloaded to pass different arguments to the object.

Overriding vs. overloading

Overloading means having methods with same name but different signature
Overriding means rewriting the virtual method of the base class

What do you mean by binding? Static vs. dynamic binding

Binding means connecting the function call to a function implementation.

Connecting the function call to the function implementation before execution is static binding whereas connection them at the run-time is dynamic binding

Define abstract class.

A class whose object can't be created is abstract class. You can create a class as abstract by declaring one or more virtual functions to pure.

Pure virtual functions are declared as below

virtual void show() = 0 ;

Previous Part3

Question - Define private, protected and public access control.

Answer
Private
Private is the default access specifier for every declared data item in a class. Private data belongs to the same class in which it is created and can only be used by the other members of the same class.

Protected
When a data item is declared as protected it is only accessible by the derived class member.

Public
Public allows to use the declared data item used by anyone from anywhere in the program. Data items declared in public are open to all and can be accessed by anyone willing to use their values and functions they provide.

Question - What are the characteristics of Object Oriented programming language?

Answer
Some key features of the Object Oriented programming are:

• Emphasis on data rather than procedure
• Programs are divided into entities known as objects
• Data Structures are designed such that they characterize objects
• Functions that operate on data of an object are tied together in data structures
• Data is hidden and cannot be accessed by external functions
• Objects communicate with each other through functions
• New data and functions can be easily added whenever necessary
• Follows bottom up design in program design

Question - What are the basic Concepts used in the Object-Oriented Programming language?

Answer

Object
Class
Data Abstraction and Encapsulation
Polymorphism
Inheritance
Message passing
Dynamic binding

Question - What is Turbo C++?

Answer
Turbo C++ provides an environment called IDE (Integrated Development Environment). The editor is used to create the source file, compile it, link it and then execute it.

Question - How to control the number of chars read in a string by using scanf()?

Answer
By using the a format specifier

char buf[25];
scanf("%20s", buf);

Doing this limits the length of the characters that will be read by scanf() to 20 characters maximum although the buffer can hold 25 characters.

Question - How to detect an end of a file?

Answer
You can either use the ifstream object ‘fin’ which returns 0 on an end of file or you can use eof() which is a member function of the ios class. It returns a non zero value on reaching the end of file.

Describe the virtual function and virtual function table.

A virtual function in C++ is

- A simple member function of a class which is declared with “virtual” keyword
- It usually performs different functionality in its derived classes.
- The resolving of the function call is done at run-time.

Virtual Table:

A virtual table is a mechanism to perform dynamic polymorphism i.e., run time binging. Virtual table is used to resolve the function calls at runtime. Every class that uses virtual functions is provided with its own virtual functions.

Every entry in the virtual table is a pointer that points to the derived function that is accessible by that class. A hidden pointer is added by a compiler to the base class which in turn calls *_vptr which is automatically set when an instance of the class is created and it points to the virtual table for that class.

What are recursive functions? What are the advantages and disadvantages of Recursive algorithms?

A recursive function is a function which calls itself.

The advantages of recursive functions are:

-Avoidance of unnecessary calling of functions.
-A substitute for iteration where the iterative solution is very complex. For example to reduce the code size for Tower of Honai application, a recursive function is bet suited.
- Extremely useful when applying the same solution

The disadvantages of Recursive functions:

-A recursive function is often confusing.
-The exit point must be explicitly coded.
-It is difficult to trace the logic of the function.

What is the difference between an external iterator and an internal iterator? Describe an advantage of an external iterator.

An internal iterator is implemented by the member functions of the class which has the iteration logic.
An external iterator is implemented by a separate class which can be attached to the object which has iteration logic.
The advantage of external iterator is that, many iterators can be made active simultaneously on the existing or same object.

Explain passing objects by reference, passing objects by value and passing objects by pointer.

Pass by value:

The callee function receives a set of values that are to be received by the parameters. All these copies of values have local scope, i.e., they can be accessed only by the callee function. The simplicity and guarantee of unchanging of values passed are the advantages of pass by value.

Pass by reference:

The callee function receives a set of references which are aliases to variables. If a change is made to the reference variable, the original value (passed by the caller function) will also be changed. All the references are handled by the pointers. Multiple values modification can be done by passing multiple variables.

Pass by pointer:

The callee function receives a pointer to the variable. The value of the pointer in the caller function can then be modified. The advantages of this process are that the changes are passed back to the caller function and multiple variables can be changed.

Explain the concepts of Throwing and catching exceptions with an example using C++.

C++ provides a mechanism to handle exceptions which occurs at runtime. C++ uses the keywords – throw, catch and try to handle exception mechanism. An entity called an exception class need to be created.

The application should have a separate section called catch block. The code in which an exception is predicted is authored in the try block.

The following code illustrates to handle the exception.

#include
class Excep {
public:
const char* error;
Excep(const char* arg) : error(arg) { }
};

class Test {
public:
int i;
// A function try block with a member initializer
Test() try : i(0) {
throw Excep("Exception thrown in A()");
}
catch (Excep& e) {
cout <<>

// A function try block
void f() try {
throw E("Exception thrown in f()");
}
catch (Excep& e) {
cout <<>

The following is the output of the above example:
Exception thrown in f()
Exception thrown in g()
Exception thrown in A()

What is an abstraction and why is it important?

Abstraction is to specify what to do (the necessary details) but not how to do (all details). For example, monitor information like size, screen type, power switches are specified for abstraction. But the inner parts and the functionality need not be known. In other words, making the details available for the user does matters.

For example, Employee class has a method calculateSalary() which receives the ‘empid’ as parameter and returns the salary of the employee concerned. The user who invokes the calculateSalary() method does not concerned about how the salary calculated. So, abstraction specifies to expose only the details which are concerned with the user.

Abstraction is important because, the code reusability is one of the benefits to the user. There is flexibility to implement the business logic for various objects which accesses the method. In the above example, salaries of employees of various cadres can use the neither same method with minor nor changes.

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Question - When do you use :: Operator in C++?

Answer - :: is the scope resolution operator. When local variable and global variable are having same name, local variable gets the priority. C++ allows flexibility of accessing both the variables through a scope resolution operator.

Question - Define reference variable in C++.

Answer - A reference variable is just like pointer with few differences. It is declared using & operator. A reference variable must always be initialized. The reference variable once defined to refer to a variable can’t be changed to point to other variable. You can't create an array of references the way it is possible with pointer.

Question - What is const qualifier?

Answer - const qualifier is used to specify the variable that can’t be change throughout the program. Variable with const qualifier is often named in uppercase.

Question - When do you use bool data type?

Answer - The bool data type can take only two values true or false.

Question - What is function overloading in C++?

Answer - You can have multiple functions with same name using function overloading facility of C++. You can use same name for multiple functions when all these functions are doing same thing.

Question - What is operator overloading in C++?

Answer - With this facility in C++, you can give additional meaning to operators.

Question - Define Inline Function.

Answer - When the function is defined Inline, the C++ compiler puts the function body inside the calling function. You can define function as Inline when the function body is small and need to be called many times, thus reduces the overhead in calling a function like passing values, passing control, returning values, returning control.

Question - Define class using C++.

Answer - A class holds the data and functions that operate on the data. It serves as the template of an object.

Question - When do you use this pointer?

Answer - 'this pointer' is used as a pointer to the class object instance by the member function. The address of the class instance is passed as an implicit parameter to the member functions.

Question - What is new and delete operator?

Answer - In C++, when you want dynamic memory, you can use operator new. It returns a pointer to the beginning of the new block of memory allocated. It returns a pointer to the beginning of the new block of memory allocated.

When memory allocated by new operator is no longer required, it is freed using operator delete.

Question - Define local class in C++.

Answer - Local class is define within the scope of a function and nested within a function.
E.g.
int func1()
{
class localclass1
{.....};
}

Question - Define namespace in C++.

Answer - Namespaces groups together entities like classes, objects and functions under a name. Namespaces provide a way to avoid name collisions of variables, types, classes or functions. Namespaces reduces the use of nested class thus reduces the inconvenience of handling nested class.

Question - What is the default access level?

Answer - The access privileges in C++ are private, public and protected. The default access level assigned to members of a class is private. Private members of a class are accessible only within the class and by friends of the class. Protected members are accessible by the class itself and its sub- classes. Public members of a class can be accessed by anyone.

Question - Explain friend class in C++.

Answer - When a class declares another class as its friend, it is giving complete access to all its data and methods including private and protected data and methods to the friend class member methods. Friendship is one way only, which means if A declares B as its friend it does NOT mean that A can access private data of B. It only means that B can access all data of A.

Question - What is virtual function?

Answer - Virtual function is the member function of a class that can be overriden in its derived class. It is declared with virtual keyword. Virtual function call is resolved at run-time (dynamic binding) whereas the non-virtual member functions are resolved at compile time (static binding).

Question - Define default constructor.

Answer - Default constructor is the constructor with no arguments or all the arguments has default values.

Question - Define abstraction.

Answer - The process of hiding unnecessary data and exposing essential features is called abstraction. Abstraction is separating the logical properties from implementation details.

Question - What is overriding?

Answer - Defining a function in the derived class with same name as in the parent class is called overriding. In C++, the base class member can be overridden by the derived class function with the same signature as the base class function. Method overriding is used to provide different implementations of a function so that a more specific behavior can be realized.

Question - What is copy constructor?

Answer - A copy constructor is a special type of constructor that is used to create an object as a copy of an existing object. It takes an argument which is a reference to the object to be copied.

Previous Part 1 Next Part 3

When dynamic checking is necessary?

Answer : Dynamic checking is necessary in the following scenarios:

• Whenever the definition of a variable is not necessary before its usage.
• When implicit conversion of variables into other types.
• When the program is to be compiled independently as there is no type checking at compile time.

What are the main differences between Java and C++?

The main differences between Java and C++ are

• Pointers are supported by C++, where as Java does not pointers.
• Operator overloading and multiple inheritance are supported by java where as Java does not.
• Java is a platform independent language, where as C++ depends on different platforms and machines.
• Java utilizes both compiler and interpreter, where as C++ is only compiler.
• Java has data type boolean, where as C++ does not.

Define structured programming.

Answer - Structured programming techniques use functions or subroutines to organize the programming code. The programming purpose is broken into smaller pieces and organized together using function. This technique provides cleaner code and simplifies maintaining the program. Each function has its own identity and isolated from other, thus change in one function doesn’t affect other.

Question - Explain Object oriented programming.

Answer - Object oriented programming uses objects to design applications. This technique is designed to isolate data. The data and the functions that operate on the data are combined into single unit. This unit is called an object. Each object can have properties and member functions. You can call member function to access data of an object. It is based on several techniques like encapsulation, modularity, polymorphism, and inheritance.

Question - What is function prototype in C++?

Answer - A function prototype is a declaration of a function that omits the function body. It specifies the function's name, argument types and return type. E.g. int add(int,int)

Question - What are the ways to comment statement in C++?

Answer - C++ supports two types of comments.
/* */ is used for commenting a block of code.
// is used for single line comments.

Question - Define Structure in C++.

Answer - The C++ programming technique allows defining user defined datatypes through structure. The syntax to declare structure is as follows:

struct student
{
char name[100]
char address[250]
};

Question - Define void pointer using C++.

Answer - In C++, void represents the absence of type, so void pointers are pointers that point to a value that has no type. The void pointers can point to any data type.
We can declare void pointer as follows.
Void *p;

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