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Top C++ Interview Questions and Answers

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C++ is a programming language that is implemented on a wide variety of operating system platforms and used for hardware design. </div>
 
This language has following features: 
Compiled, Statically typed, Multi-paradigm and Free-form. 
 
This Language also consists of both high-level and low-level language features. 
 
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Here is a list of C++ Interview questions with answers which are asked at the time of campus interviews, placements. 
 
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Top C++ Interview Questions and Answers for freshers and experienced are below are below ::</h3>
 
1. What is C++? 
C++ is created by Bjarne Stroustrup of AT&T Bell Labs as an extension of C, C++ is an object-oriented computer language used in the development of enterprise and commercial applications. 
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Microsoft’s Visual C++ became the premier language of choice among developers and programmers. 
 
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2. What is polymorphism? Explain with an example?</div>
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"Poly" means "many" and "morph" means "form". Polymorphism is the ability of an object (or reference) to assume (be replaced by) or become many different forms of object. 
 
Example: function overloading, function overriding, virtual functions. Another example can be a plus ‘+’ sign, used for adding two integers or for using it to concatenate two strings.</div>
 
3. What is the difference between C & C++? 
C++ is an object oriented programing but c is a procedure oriented programing. C is super set of C++. </div>
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C can’t support inheritance, function overloading, method overloading etc. but C++ can do this. </div>
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In c-program the main function could not return a value but in the C++ the main function should return a value. 
 
4. What is a class? 
Class is a user-defined data type in C++. It can be created to solve a particular kind of problem. After creation the user need not know the specifics of the working of a class. 
 
5. What is the difference between class and structure? 
By default, the members of structures are public while that tor class is private. 
Structures doesn’t provide something like data hiding which is provided by the classes. 
Structures contains only data while class bind both data and member functions. 
 
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6. Define Constructors? 
A constructor is a member function with the same name as its class. The constructor is invoked whenever an object of its associated class is created. It is called constructor because it constructs the values of data members of the class. 
 
7. What is the difference between a copy constructor and an overloaded assignment operator? 
A copy constructor constructs a new object by using the content of the argument object. An overloaded assignment operator assigns the contents of an existing object to another existing object of the same class. 
 
8. What do you mean by implicit conversion? 
Whenever data types are mixed in an expression then C++ performs the conversion automatically. 
Here smaller type is converted to wider type. 
 
Example : in case of integer and float integer is converted into float type. 
 
9. What is dynamic binding? 
Dynamic binding (also known as late binding) means that the code associated with a given procedure call is not known until the time of the call at run time. It is associated with polymorphism and inheritance. 
 
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10. What is the difference between an object and a class?</div>
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I. Classes and objects are separate but related concepts. 
Every object belongs to a class and every class contains one or more related objects. 
 
II. A Class is static. All of the attributes of a class are fixed before, during, and after the execution of a program. The attributes of a class don't change. 
 
The class to which an object belongs is also (usually) static. If a particular object belongs to a certain class at the time that it is created then it almost certainly will still belong to that class right up until the time that it is destroyed. 
 
III. An Object on the other hand has a limited lifespan. Objects are created and eventually destroyed. Also during that lifetime, the attributes of the object may undergo significant change.</div>
 
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11. What is public, protected, private? 
Public, protected and private are three access specifiers in C++. 
Public data members and member functions are accessible outside the class. 
Protected data members and member functions are only available to derived classes. 
Private data members and member functions can’t be accessed outside the class. However there is an exception can be using friend classes. 
 
12. In C++, what is the difference between method overloading and method overriding? 
Overloading a method (or function) in C++ is the ability for functions of the same name to be defined as long as these methods have different signatures (different set of parameters). Method overriding is the ability of the inherited class rewriting the virtual method of the base class. 
 
13. What is difference between function overloading and operator overloading? 
A function is overloaded when same name is given to different function. 
While overloading a function, the return type of the functions need to be the same. 
 
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Function overloading: C++ enables several functions of the same name to be defined, as long as these functions have different sets of parameters (at least as far as their types are concerned). This capability is called function overloading. When an overloaded function is called, the C++ compiler selects the proper function by examining the number, types and order of the arguments in the call. Function overloading is commonly used to create several functions of the same name that perform similar tasks but on different data types.</div>
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Operator overloading allows existing C++ operators to be redefined so that they Customer is king inc., 
 
work on objects of user-defined classes. Overloaded operators are syntactic sugar for equivalent function calls. They form a pleasant facade that doesn't add anything fundamental to the language (but they can improve understandability and reduce maintenance costs).</div>
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14. Define inheritance? 
The mechanism of deriving a new class (derived) from an old class (base class) is called inheritance. It allows the extension and reuse of existing code without having to rewrite the code from scratch. Inheritance is the process by which objects of one class acquire properties of objects of another class. 
 
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advantages of inheritance : It permits code reusability. Reusability saves time in program development. Itencourages the reuse of proven and debugged high-quality software, thus reducing 
problem after a system becomes functional.</div>
 
15. What is friend function? 
The function declaration should be preceded by the keyword friend. The function definitions does not use either the keyword or the scope operator ::. The functions that are declared with the keyword friend as friend function. Thus, a friend function is an ordinary function or a member of another class. 
 
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16. What are virtual functions? 
A virtual function allows derived classes to replace the implementation provided by the base class. The compiler makes sure 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. This allows algorithms in the base class to be replaced in the derived class, even if users don't know about the derived 
class. 
 
17. What do you mean by pure virtual functions? 
A pure virtual member function is a member function that the base class forces derived classes to provide. Normally these member functions have no implementation. Pure virtual functions are equated to zero. 
class Shape { public: virtual void draw() = 0; }; 
 
18. What is an iterator? 
Iterators are like pointers. They are used to access the elements of containers thus providing a link between algorithms and containers. Iterators are defined for specific containers and used as arguments to algorithms. 
 
19. What are the differences between new and malloc? 
New initializes the allocated memory by calling the constructor. Memory allocated with new should be released with delete. 
 
Malloc allocates uninitialized memory. 
 
The allocated memory has to be released with free. New automatically calls the constructor while malloc (doesn’t). 
 
20. What is an explicit constructor? 
A conversion constructor declared with the explicit keyword. The compiler does not use an explicit constructor to implement an implied conversion of types. It’s purpose is reserved explicitly for construction. Explicit constructors are simply constructors that cannot take part in an implicit conversion. 
 
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21. What do you mean by inline function? 
An inline function is a function that is expanded inline when invoked.ie. the compiler replaces the function call with the corresponding function code. An inline function is a function that is expanded in line when it is invoked. That is the compiler replaces the function call with the corresponding function code (similar to macro). 
 
22. What is the difference between a copy constructor and an overloaded assignment operator? 
A copy constructor constructs a new object by using the content of the argument object. An overloaded assignment operator assigns the contents of an existing object to another existing object of the same class. 
 
23. What is class invariant? 
A class invariant is a condition that defines all valid states for an object. It is a logical condition to ensure the correct working of a class. Class invariants must hold when an object is created, and they must be preserved under all operations of the class. In particular all class invariants are both preconditions and post-conditions for all operations or member functions of the class. 
 
24. What is a scope resolution operator?</div>
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A scope resolution operator (::), can be used to define the member functions of a class outside the class. 
 
25. What does extern mean in a function declaration? 
It tells the compiler that a variable or a function exists, even if the compiler hasn’t yet seen it in the file currently being compiled. This variable or function may be defined in another file or further down in the current file. 
 
26. Describe the main characteristics of static functions. 
The main characteristics of static functions include, 
 
It is without the a this pointer, 
It can't directly access the non-static members of its class 
It can't be declared const, volatile or virtual. 
It doesn't need to be invoked through an object of its class, although for convenience, it may.</div>
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Top C++ Interview Questions and Answers

C++ is a programming language that is implemented on a wide variety of operating system platforms and used for hardware design. This l...

Top 20 OOPs Interview Questions and Answers for Fresher

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Object-oriented programming (OOP) is a programming paradigm that represents the concept of "objects" that have data fields (attributes that describe the object) and associated procedures known as methods.</div>
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Top 20 OOPs Interview Questions and Answers for freshers and experienced are below are below :</h3>
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1. What is Object Oriented Programming ? 
It is a problem solving technique to develop software systems. It is a technique to think real world in terms of objects. Object maps the software model to real world concept. These objects have responsibilities and provide services to application or other objects. 
 
2. What is a Class ? 
A class describes all the attributes of objects, as well as the methods that implement the behavior of member objects. It is a comprehensive data type which represents a blue print of objects. It’s a template of object. 
 
3. What is an Object ? 
It is a basic unit of a system. An object is an entity that has attributes, behavior, and identity. Objects are members of a class. Attributes and behavior of an object are defined by the class definition. 
 
4. What is the relation between Classes and Objects? 
--> They look very much same but are not same. Class is a definition, while object is instance of the class created. Class is a blue print while objects are actual objects existing in real world. Example we have class CAR which has attributes and methods like Speed, Brakes, Type of Car etc.Class CAR is just a prototype, now we can create real time objects which can be used to provide functionality. Example we can create a Maruti car object with 100 km speed and urgent brakes. 
 
5. What are different properties provided by Object-oriented systems ? 
Following are characteristics of Object Oriented System’s:- 
 
Abstraction: It allows complex real world to be represented in simplified manner. Example color is abstracted to RGB.By just making the combination of these three colors we can achieve any color in world. It’s a model of real world or concept. 
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Encapsulation: The process of hiding all the internal details of an object from the outside world. 
 
Communication: Using messages when application wants to achieve certain task it can only be done using combination of objects. A single object can not do the entire task. Example if we want to make order processing form. We will use Customer object, Order object, Product object and Payment object to achieve this functionality. In short these objects should communicate with each other. This is achieved when objects send messages to each other. 
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Object lifetime: All objects have life time. Objects are created, initialized, necessary functionalities are done and later the object is destroyed. Every object have there own state and identity, which differ from instance to instance. 
 
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6. What is an Abstract class ? 
Abstract class defines an abstract concept which can not be instantiated and comparing o interface it can have some implementation while interfaces can not. 
 
Below are some points for abstract class:- 
=>We can not create object of abstract class it can only be inherited in a below class. 
=> Normally abstract classes have base implementation and then child classes derive from the abstract class to make the class concrete. 
 
7. What are Abstract methods? 
Abstract class can contain abstract methods. Abstract methods do not have implementation. Abstract methods should be implemented in the subclasses which inherit them. 
 
So if an abstract class has an abstract method class inheriting the abstract class should implement the method or else java compiler will through an error. 
 
In this way, an abstract class can define a complete programming interface thereby providing its subclasses with the method declarations for all of the methods necessary to implement that programming interface. 
 
Abstract methods are defined using "abstract" keyword. Below is a sample code snippet. 
abstract class pcdsGraphics 
{ 
abstract void draw(); 
} 
 
Any class inheriting from "pcdsGraphics" class should implement the "draw" method or else the java compiler will throw an error. so if we do not implement a abstract method the program will not compile. 
 
8. What is the difference between Abstract classes and Interfaces ? 
Difference between Abstract class and Interface is as follows:- 
(a). Abstract class can only be inherited while interfaces can not be it has to be implemented. 
(b). Interface cannot implement any methods, whereas an abstract class can have implementation. 
(c). Class can implement many interfaces but can have only one super class. 
(d). Interface is not part of the class hierarchy while Abstract class comes in through inheritance. 
(e). Unrelated classes can implement the same interface. 
 
9. What is difference between Static and Non-Static fields of a class ? 
Non-Static values are also called as instance variables. Each object of the class has its own copy of Non-Static instance variables. 
 
So when a new object is created of the same class it will have completely its own copy of instance variables. While Static values have only one copy of instance variables and will be shared among all the objects of the class. 
 
10. What are inner classes and what is the practical implementation of inner classes? 
Inner classes are nested inside other class. They have access to outer class fields and methods even if the fields of outer class are defined as private. 
 
public class Pcds 
{ 
class pcdsEmp 
{ 
// inner class defines the required structure 
String first; 
String last; 
} 
// array of name objects 
clsName personArray[] = {new clsName(), new clsName(), new clsName()}; 
} 
 
Normally inner classes are used for data structures like one shown above or some kind of helper classes. 
 
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11. What is a constructor in class? 
Constructor has the same name as the class in which it resides and looks from syntax point of view it looks similiar to a method. Constructor is automatically called immediately after the object is created, before the new operator completes. 
Constructors have no return type, not even void. This is because the implicit return type of a class' constructor is the class type itself. It is the constructor's job to initialize the internal state of an object so that the code creating an instance will have a fully initialized, usable object immediately. 
 
12. Can constructors be parameterized? 
Yes we can have parameterized constructor which can also be termed as constructor overloading. Below is a code snippet which shows two constructors for pcdsMaths class one with parameter and one with out. 
class pcdsMaths 
{ 
double PI; 
// This is the constructor for the maths constant class. 
pcdsMaths() 
{PI = 3.14;} 
pcdsMaths(int pi) 
{ 
PI = pi; 
} } 
 
13. What is the use if instanceof keyword? and How do refer to a current instance of object? 
"instanceof" keyword is used to check what is the type of object. 
we can refer the current instance of object using "this" keyword. For instance if we have class which has color property we can refer the current object instance inside any of the method using "this.color". 
 
14. what is Bootstrap, Extension and System Class loader? or Can you explain primordial class loader? 
--> There three types of class loaders:- 
BootStrap Class loader also called as primordial class loader. 
Extension Class loader.  
System Class loader. 
 
Let’s now try to get the fundamentals of these class loaders. 
 
Bootstrap Class loader : Bootstrap class loader loads those classes those which are essential for JVM to function properly. Bootstrap class loader is responsible for loading all core java classes for instance java.lang.*, java.io.* etc. Bootstrap class loader finds these necessary classes from “jdk/ jre/lib/rt.jar”. Bootstrap class loader can not be instantiated from JAVA code and is implemented natively inside JVM. 
 
Extension Class loader : The extension class loader also termed as the standard extensions class loader is a child of the bootstrap class loader. Its primary responsibility is to load classes from the extension directories, normally located the “jre/lib/ext” directory. This provides the ability to simply drop in new extensions, such as various security extensions, without requiring modification to the user's class path. 
 
System Class loader : The system class loader also termed application class loader is the class loader responsible for loading code from the path specified by the CLASSPATH environment variable. It is also used to load an application’s entry point class that is the "static void main ()" method in a class. 
 
 
15. what’s the main difference between ArrayList / HashMap and Vector / Hashtable? 
Vector / HashTable are synchronized which means they are thread safe. Cost of thread safe is performance degradation. So if you are sure that you are not dealing with huge number of threads then you should use ArrayList / HashMap.But yes you can still 
synchronize List and Map’s using Collections provided methods :- 
List OurList = Collections.synchronizedList (OurList); 
Map OurMap = Collections.synchronizedMap (OurMap); 
 
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 16. What are access modifiers? 
-->  Access modifiers decide whether a method or a data variable can be accessed by another method in another class or subclass. 
 
Four types of access modifiers:

Public : - Can be accessed by any other class anywhere. 
Protected : - Can be accessed by classes inside the package or by subclasses ( that means classes who inherit from this class). 
Private :- Can be accessed only within the class. Even methods in subclasses in the same package do not have access. 
Default :- (Its private access by default) accessible to classes in the same package but not by classes in other packages, even if these are subclasses. 
 
17. Define exceptions ? 
An exception is an abnormal condition that arises in a code sequence at run time. Basically there are four important keywords which form the main pillars of exception handling: try, catch, throw and finally. 
Code which you want to monitor for exception is contained in the try block. If any exception occurs in the try block its sent to the catch block which can handle this error in a more rational manner. To throw an exception manually you need to call use the throw keyword. If you want to put any clean up code use the finally block. The finally block is executed irrespective if there is an error or not. 
 
18. What is serialization?How do we implement serialization actually? 
Serialization is a process by which an object instance is converted in to stream of bytes. There are many useful stuff you can do when the object instance is converted in to stream of bytes for instance you can save the object in hard disk or send it across the network. 
 
In order to implement serialization we need to use two classes from java.io package ObjectOutputStream and ObjectInputStream. ObjectOutputStream has a method called writeObject, while ObjectInputStream has a method called readObject. Using writeobject we can write and readObject can be used to read the object from the stream. Below are two code snippet which used the FileInputStream and FileOutputstream to read and write from harddisk.</div>
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Top 20 OOPs Interview Questions and Answers for Fresher

Object-oriented programming (OOP) is a programming paradigm that represents the concept of "objects" that have data fields (attr...

Top 20 OOPs Interview Questions and Answers

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Object-oriented programming (OOP) is a programming paradigm that represents the concept of "objects" that have data fields (attributes that describe the object) and associated procedures known as methods. 
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Top 20 OOPs Interview Questions and Answers for freshers and experienced are below are below :</h3>
 
1. What is OOPS? 
Object-oriented programming (OOP) is a programming language model organized around objects rather than "actions" and data rather than logic. Historically, a program has been viewed as a logical procedure that takes input data, processes it, and produces output data. 
 
2. basic Concepts of OOPs? 
Abstraction. 
Encapsulation. 
Inheritance. 
Polymorphism. 
 
3. What is a class? 
A set or category of things having some property or attribute in common and differentiated from others by kind, type, or quality. 
 
4. What is an object? 
Objects are created from Classes, in C#, is an instance of a class that is created dynamically. Object is also a keyword that is an alias for the predefined type System. 
 
5. What is Encapsulation? 
Encapsulation is the packing of data and functions into a single component. The features of encapsulation are supported using classes in most object-oriented programming languages, although other alternatives also exist. 
 
It allows selective hiding of properties and methods in an object by building an impenetrable wall to protect the code from accidental corruption. 
 
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6. What is Polymorphism? 
In programming languages and type theory, polymorphism is the provision of a single interface to entities of different types. 
A polymorphic type is a type whose operations can also be applied to values of some other type, or types. 
 
7. What is Inheritance? 
inheritance is when an object or class is based on another object or class, using the same implementation (inheriting from a class) specifying implementation to maintain the same behavior (realizing an interface; inheriting behavior). 
 
It is a mechanism for code reuse and to allow independent extensions of the original software via public classes and interfaces. 
 
8. What is Constructor? 
A is special method of the class that will be automatically invoked when an instance of the class is created is called as constructor. 
 
Constructors are mainly used to initialize private fields of the class while creating an instance for the class. 
 
When you are not creating a constructor in the class, then compiler will automatically create a default constructor in the class that initializes all numeric fields in the class to zero and all string and object fields to null. 
 
Syntax. 
[Access Modifier] ClassName([Parameters]) 
{ 
} 
 
9. Types of Constructors 
Basically constructors are 5 types those are 
Default Constructor 
Parameterized Constructor 
Copy Constructor 
Static Constructor 
Private Constructor 
 
10. Define Destructor? 
A destructor is a method which is automatically invoked when the object is destroyed. 
 
Its main purpose is to free the resources (memory allocations, open files or sockets, database connections, resource locks, etc.) 
 
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11. What is Inline function? 
In the C and C++ programming languages, an inline function is one qualified with the keyword inline; this serves two purposes. 
Firstly, it serves as a compiler directive, which suggests (but does not require) that the compiler substitute the body of the function inline by performing inline expansion, 
The second purpose of inline is to change linkage behavior; the details of this are complicated. 
 
12. What is operator overloading? 
In programming, operator overloading—less commonly known as operator ad hoc polymorphism—is a specific case of polymorphism, where different operators have different implementations depending on their arguments. Operator overloading is generally defined by the language, the programmer, or both. 
 
13. Different between method overriding and  method overloading? 
In Overriding methods it will create two or more methods with same name and same parameter in different classes. 
 
while Overloading it will create more then one method with same name but different parameter in same class. 
 
14. What is this keywords? 
Every instance method in every object in Java receives a reference named this when the method is invoked.  The reference named this is a reference to the object on which the method was invoked.  It can be used for any purpose for which such a reference is needed. 
 
15. What is super keyword? 
The super keyword is a reference variable that is used to refer immediate parent class object. 
 
Whenever you create the instance of subclass, an instance of parent class is created implicitly i.e. referred by super reference variable. 
 
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16. What is an abstract class?An abstract class is a class that is declared abstract—it may or may not include abstract methods. Abstract classes cannot be instantiated, but they can be subclassed. 
 
17. What is final keywords? 
The final keyword in java is used to restrict the user. The java final keyword can be used in many context. 
Final can be: variable, method, class. 
 
The final keyword can be applied with the variables, a final variable that have no value it is called blank final variable or uninitialized final variable. It can be initialized in the constructor only. The blank final variable can be static also which will be initialized in the static block only. 
 
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