assignment questions on inheritance in c

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Home » C++ programs

C++ Inheritance programs/examples

Inheritance is a feature of object oriented programming system , by which a class can inherit the commonly used properties/features of another classes. In this section you will get solved c++ programs using inheritance : simple inheritance , multiple inheritance , multilevel inheritance , hybrid inheritance , hierarchical inheritance .

We are providing here set of programs on privately and publicly inheritance.

List of C++ Inheritance programs

• C++ program to demonstrate example of simple inheritance .
• C++ program to demonstrate example of private simple inheritance .
• C++ program to read and print student's information using two classes and simple inheritance .
• C++ program to demonstrate example of multilevel inheritance .
• C++ program to read and print employee information using multiple inheritance .
• C++ program to demonstrate example of multiple inheritance .
• C++ program to demonstrate example of hierarchical inheritance to get square and cube of a number.
• C++ program to read and print employee information with department and pf information using hierarchical inheritance .

List of most popular & searched C++ programs

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• C++ program to add two integer numbers . This program will read two integer numbers from the user and calculate their addition/sum.

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Browse Course Material

Course info, instructors.

• Kyle Murray

Departments

• Electrical Engineering and Computer Science

As Taught In

• Programming Languages
• Software Design and Engineering

Learning Resource Types

Introduction to c and c++, c++ inheritance, lecture notes.

Lecture 6: C++ Inheritance (PDF)

Lab Exercises

Take a look at this example code:

Put it in a file named lab6.cpp and then compile it like this:

Verify your understanding of how the virtual keyword and method overriding work by performing a few experiments:

• Remove the virtual keyword from each location individually, recompiling and running each time to see how the output changes. Can you predict what will and will not work?
• Try making Shape::draw non-pure by removing = 0 from its declaration.
• Try changing shape (in main() ) from a pointer to a stack-allocated variable.

Assignment 6

In the file rps.cpp, implement a class called Tool . It should have an int field called strength and a char field called type . You may make them either private or protected. The Tool class should also contain the function void setStrength(int) , which sets the strength for the Tool .

Create 3 more classes called Rock , Paper , and Scissors , which inherit from Tool . Each of these classes will need a constructor which will take in an int that is used to initialize the strength field. The constructor should also initialize the type field using 'r' for Rock, 'p' for Paper , and 's' for Scissors .

These classes will also need a public function bool fight(Tool) that compares their strengths in the following way:

• Rock’s strength is doubled (temporarily) when fighting scissors, but halved (temporarily) when fighting paper.
• In the same way, paper has the advantage against rock, and scissors against paper.
• The strength field shouldn’t change in the function, which returns true if the original class wins in strength and false otherwise.

You may also include any extra auxiliary functions and/or fields in any of these classes. Run the program without changing the main function, and verify that the results are correct.

Solutions are not available for this assignment.

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Interesting Programming Exercises to Teach Inheritance?

I originally asked this over on Stack Overflow, but they suggested I look here instead:

I'm currently teaching my students about the concept of inheritance (we're using Python 3) but am unable to think up (or find) any meaningful programming exercises. Everything I seem to find online as a teaching resource rehashes the same forced examples: Employee() inherits Person() ; Dog() inherits Animal() ; etc.

While these are great ways to drive home the basics of inheritance, I can't help feeling they are a bit hollow as programming exercises. In the end I don't feel like I've made anything. Unlike, for example, the myriad of different exercises out there that can be used to teach recursion.

Anyway, I'm sorry for the rather "soft" question, but I'm just desperate for some better examples that could actually be tackled by a student who's still learning the concept. Thanks.

• lesson-ideas
• object-oriented-paradigm

• 4 $\begingroup$ Congratulations on asking a HNQ on our site. And welcome to CSEducators. $\endgroup$ –  Buffy Commented May 1, 2018 at 20:08
• 15 $\begingroup$ As a student, I didn't understand inheritance as anything other than an academic exercise, until I started looking at GUI toolkits, with classes like BaseView, GridView, ListView, OrderedListView, etc; and started making my own extensions of these things, that it really made sense. $\endgroup$ –  nexus_2006 Commented May 1, 2018 at 21:15
• 2 $\begingroup$ Inheritance is important, but not as important as interfaces. While I disagree with the assertion that inheritance is a way to get around the absence of templates that c++ offers, I agree that it is over emphasized in teaching OO programming. 90% of the objects you will make outside of a GUI are descended only from Object. $\endgroup$ –  pojo-guy Commented May 2, 2018 at 0:25
• 2 $\begingroup$ @pojo-guy: Interfaces are a variation on inheritance. Assuming you know neither, inheritance is easier to understand than interfaces. The use case for interfaces is rather complex, compared to the use case for inheritance. Regardless of which will be used more often in a professional context, education should follow a logical progression that makes every step as light as it can be. $\endgroup$ –  Flater Commented May 2, 2018 at 12:46
• 3 $\begingroup$ The best thing you can probably teach about inheritance is to avoid it until it makes absolutely perfect sense (and probably even then). The reason it's hard to find a good teaching example of inheritance is because it's very difficult to find models that really should use inheritance. In the end I've regretted every non-trivial use of inheritance, some trivial ones work out pretty well though. What I've found is that if there is any question whatsoever, choose composition/encapsulation, even if the objects easily pass the "is a" test. $\endgroup$ –  Bill K Commented May 3, 2018 at 19:51

14 Answers 14

I'm not as familiar with Python as I am with other languages, but I'm sure your students have played Minecraft.

If you haven't, I suggest taking a few minutes to find some introductory "Lets Play" videos on YouTube first.

Let's talk Blocks.

Minecraft has dozens of blocks. Dirt, some, water, colored wool...

All blocks can be broken, picked up, placed, stacked, stored in chests, and crafted together. But not all blocks do just those things.

The chest let's the player store items in it. The furnace smelts some blocks into other blocks. Grass, when broken, drops a completely different block. Stone doesn't drop anything at all unless dug out with a pickaxe.

Minecraft can do this because of all of those basic methods that subclasses inherit and override.

Take this method (not pulled from source, just based on):

The default implementation puts a single item (the block itself) into a list and returns it.

BlockGrass would put dirt into the list instead.

BlockStone would check to make sure that harvest is true and the put cobblestone in the list.

BlockDiamondOre checks harvest and fortune , putting a different number of diamond items into the list, even determining how many based on the Random supplied.

There are roughly 100 different methods in the block class to handle all of the possible functionality. Update ticks (crops), neighbor updates (observer, torches), interaction (doors, chest, furnace, crafting bench), whether or not a block has a tile entity (chest, furnace), and on and on and on. Most of them are blank and do nothing, entirely up to the derived class to add to, if it needs it.

The same goes for items, some of which (like sticks) don't even have a derived class of their own because they do nothing special. They just exist and do everything any item can.

This is why the are so many mods for Minecraft that add so many new things: no one 1 has to implement anything special in order for everything to Just Work.

1 Well, except Minecraft Forge, who maintain the official unofficial mod API. But Forge is a special kind of magic that isn't important here

• 8 $\begingroup$ I don't really care for Minecraft, but I like this answer a lot. One thing that bothers me with those standard Animal=>Dog examples is that it's trying to explain an abstract concept with a slightly less abstract example - but to what end does an Animal even need a MakeNoise() function? Instantly obvious with a "real life" example like this: A sound effect needs to be played when the player is close. Also it's very easy to make some screenshots to illustrate concepts, which can make those olde lecture slides more interesting and easier to understand. $\endgroup$ –  R. Schmitz Commented May 2, 2018 at 10:05
• 3 $\begingroup$ Yep. I think looking at game related examples is a very good idea because OO is important for game design and it is easy to imagine the code being actually used. I think the block example can get quite complex though. Maybe just define some game objects with a shared draw method, an image etc. Add something like health in the mix and you're done. OP could take a look at py.processing.org and you can even easily draw stuff. Maybe idk snow that turns into rain after a couple of seconds of falling? (position, speed, lifetime, image) and rain falls faster than snow $\endgroup$ –  AmazingDreams Commented May 2, 2018 at 10:55
• 3 $\begingroup$ @Flater I have to admit I'm a bit confused now. I thought it's pretty clear that that was a rhetoric question. Even if you take it as a literal question, your example for MakeNoise() isn't about MakeNoise() at all. And then, the actual example is another slightly less abstract example / spherial cow , when my whole point was that I like this answer because it is 100% concrete. $\endgroup$ –  R. Schmitz Commented May 2, 2018 at 14:00
• 2 $\begingroup$ @Flater stumble over the name ? I'll just assume you meant to change more than the name, because Feed is a really bad name for a function which is supposed to produce animal noises. What I like about this answer is how it uses exactly a concrete example of programming , which can easily demonstrate how - to keep with your metaphor - some trees together make up part of a real wood/forest. $\endgroup$ –  R. Schmitz Commented May 2, 2018 at 14:55
• 1 $\begingroup$ @Flater I did not engage your cheap stabs like "Failure to understand..." or the first half of this comment now and I will continue to do so, because that feels like trolling behaviour to me. For the second part of your comment: We probably just apply different definitions of "concrete" here. For me, it's not concrete because you didn't get that from actual code used in production - I really don't see any remarkable difference to the standard Animal=>Dog or Person=>Employee examples mentioned by OP. You will have another reasoning why you think it is concrete. $\endgroup$ –  R. Schmitz Commented May 2, 2018 at 15:46

Too many examples that you find are (IMO) fatally flawed. The Animal->Dog is especially flawed, though widely used. The problem is that these sorts of examples almost require that the superclass has a certain set of public methods that isn't the same as that of the subclass, requiring you to add additional public methods to the subclass. This is because an object of the subclass has different behavior than that of the superclass. This leads to poor design. If, when you create a variable you think of it as an Animal (or in a statically typed language declare it so) then later, when you assign a Dog object to the same variable you, the programmer have to remember that it is now a dog so that it can accept the sit() method that wasn't implemented in Animal.

In a dynamically typed language like Python, the programmer has to remember types since the compiler doesn't, but if you also have to remember where in an inheritance hierarchy an object is at runtime then you have a more difficult than necessary task. You can ask an object for its type of course, but that leads to messy code.

A better solution is to maintain the set of methods declared in the topmost class as you descend and not extend them. What you change in the subclass is only the implementations of methods defined in the superclass. Then your original intention (it is an Animal) doesn't need to be modified (and mentally maintained) as you write the program. The variable responds only to Animal methods, clearly impossible in this example.

One way to help solve your problem is to assure that your inheritance hierarchies are very (very) shallow. Don't try to define things three or four deep. This helps even if you do add additional public methods in a subclass.

However, there is a better way.

One reason for building hierarchies is to get different behavior in the subclass. But there is a better way to do that. And it doesn't require adding additional behaviors. The flaw in thinking is that many people think of using inheritance hierarchies for BIG things. Like Dogs and Giraffes. If instead you don't use inheritance for the big things but only for small things, life gets easier.

The alternative to inheritance I suggest is to build objects by composition . Complex (i.e. big) things are made up of smaller parts that are themselves complex (objects, not integers and strings). This leads to programming by delegation . An object can delegate some of its behavior to another object, possibly held in a field and invisible to the public class's clients. When a public method of the class is invoked, it simply sends a message to the delegate object and can get a return value that it can return or modify.

So the makeNoise() method of Animal looks like this.

The object in myNoiseMaker makes the actual sound. But by changing that object the Animal can bark or meow or roar or what ever is needed for that animal. The value can be set in a constructor to produce a Dog or a Lion, of course. All animals behave the same (same set of public methods) but each in its own way. Don't start thinking that we need switch statements to achieve this. There is no test for the kind of thing we are. One possible value of myNoiseMaker only knows how to bark. A different object knows how to roar. We just create (or replace) the object as needed.

This of course is well known as the Strategy Design Pattern. The strategy here is an object with one method: shout() .

It is also possible to use inheritance at this level and one Strategy can inherit from another. Usually you want a Strategy that implements shout as a no-op. You can inherit from this to create a Dog and from that to create a LoudDog. So an object built by composition (lots of Strategies) and using Delegation is pretty rich and very flexible. Each instantiation of an Animal object only knows how to do one thing as appropriate. This is polymorphism, actually.

But, once you grasp the idea of a Strategy you can do much more. As a program runs, its state changes. One possible way to develop programs is with State Change Diagrams. At certain state changes it is possible to replace one delegate with another, changing the behavior of the containing object that uses delegation. For example, the first time you press a number key on a calculator it shows that value in the display. But the next time you press it something different happens and the new value is accumulated into the old. So pressing a number key after pressing the equals key has different behavior than after pressing a number key. This can be handled by having the calculator delegate the key presses to (various) strategy objects as the state changes. Again, you don't need flags and switch statements to remember what to do next. The Strategy object knows what to do since it was designed to do only that one thing.

To go even farther, another design pattern is Decorator. There are various kinds of decorator but the essence is that it is a certain kind of thing and it also has something of the same kind. A Strategy Decorator is a strategy (it has the shout method) and it also has a strategy as a field. When the containing object delegates to the Decorator it can first fire the shout method of the held object and and also add a sound of its own. Since a Decorator is a Strategy it can also decorate another decorator as the held object. This is essentially a linked list of Strategies with all but the last being a Strategy Decorator.

So, you can illustrate inheritance and dynamic polymorphism very nicely with small classes such as strategies and decorators. But it requires a mental model about how to build objects - use composition primarily (for the big things) and inheritance for the small things.

And notice that this mechanism (composition + delegation) moves the focus of change-of-behavior from the class to the individual object.

To more explicitly answer your question, you could provide a basic class in which a few methods delegate to other objects and then have them make the behavior of objects more interesting by defining other delegates that inherit from the ones you give. The first cut could have all of the delegates provide empty behavior. Rather than modifying the classes of those objects, have them write (simple) subclasses.

I'll note in also that a statically typed language such as Java can do even better here, since the explicit declarations of the variable types, unavailable in Python and Ruby, makes it clear about what is a Strategy and what is not. In general, though a Strategy is very simple, a method or two, named for the task at hand.

Let me try to explain why it is a bad idea, especially in statically typed languages like Java but also in Python, to define new public methods in a subclass or in classes that implement an interface.

Suppose you have the following: Animal (either a base class or an interface, and you have Mammal and Invertebrate as subclasses of Animal. You also have Dog and Kangaroo as subclasses of Mammal and Mosquito as a subclass of Invertebrate. Suppose also that each class introduces new public methods not defined in its superclass. The sensible programmer will of course create a Dog object with

and other objects similarly. Now myPet.sit(); makes perfect sense whereas had myPet been given the static type Animal it would not.

However, the problem arises when you create collections, say List, or pass myPet as an argument to a method that expects an Animal. What can you do in that method? What can you do with objects extracted from the List? The compiler only knows the object as Animal, of course, so you can invoke those methods, but what if you want to do more with the object. Runtime type checking (instanceof) and Casting can recover the specific type but at the cost of potential runtime errors if you make inappropriate assumptions. The original programmer may not make such errors in a small program, but the problem becomes very difficult in a large, important, and maintained-by-others program. It isn't the original declaration that is the issue here. Of course you say Dog. Or do you?

A very common idiom in Java is to declare an ArrayList as follows

Note the interface type on the LHS and a specific class type on the RHS. This makes it easy to replace the concrete type with a different one without changing the LHS or the code that follows. This is actually the preferred method of doing such declarations.

Why does it work? It works because all of the provided implementers of List have, as their only public methods, the methods defined in List itself. It wouldn't work if that were not the case. Then, if additional methods were defined (and used), changing the concrete type would become much more difficult.

The good practice in the libraries (not adding public methods) is good for a reason. I'm simply suggesting it as a general practice that makes for better programs. It is also a simple and safe rule for beginners to learn. The rule is frequently broken, I realize. But poorly designed software is frequently written, also.

And note that this problem is more severe in Python, which is dynamically typed and variables (identifiers) have no type at all. Java declarations at least give you some sort of managed knowledge of what sort of thing is referenced. In Python (Ruby) you need to do that yourself or include frequent type checks or suffer frequent errors.

• 14 $\begingroup$ "This leads to poor design. If, when you create a variable you think of it as an Animal (or in a statically typed language declare it so) then later, when you assign a Dog object to the same variable you, the programmer have to remember that it is now a dog so that it can accept the sit() method that wasn't implemented in Animal." Are you sure you're doing this right? If you wanted a variable pointing to a dog, you'd declare it as a Dog . When all you want is an Animal , you don't want to call sit() on it. $\endgroup$ –  user541686 Commented May 1, 2018 at 20:42
• 2 $\begingroup$ @Buffy if your goal is consistent interfaces you'd use an interface and have each animal implement that instead of using inheritance... $\endgroup$ –  enderland Commented May 1, 2018 at 23:07
• 5 $\begingroup$ At my university, they went with Point->LineSegment->Triangle->Quadrilateral inheritance...I got into major fight with professor when trying to argue with him that he is scarring the minds of students. $\endgroup$ –  Artur Biesiadowski Commented May 2, 2018 at 11:43
• 2 $\begingroup$ @Buffy: Your comment does seem wrong. If you define an Animal variable, you should never care about which animal it is. The problem is being created by the developer that decided to declare an Animal instead of a Dog variable. You say the problem is unavoidable, but I strongly disagree here. The problem is the expectation of the developer after needlessly downcasting their type to the subclass. That is developer error, not an inherent design flaw. $\endgroup$ –  Flater Commented May 2, 2018 at 13:02
• 2 $\begingroup$ @KevinKrumwiede, too strong. Python is an excellent teaching language, but you have to program it like Python, not like Java. If you follow simple rules in Python you get great results. But the same is true for Java or other languages. Programming naively in any language can lead to design-disaster. And thinking in one language while programming in another seldom leads to good results. Learn your tools, just as any crafts-person should. $\endgroup$ –  Buffy Commented May 4, 2018 at 11:58

I've got one that might help, modified/simplified from an actual problem I had to solve at my current job.

Imagine you're writing a Content Management system - this system will store four types of documents (and the Meta/Index information for them)

• PDFs (who created, description, file size)
• Word documents (who created, description, file size)
• Pictures (who created, description, image dimensions, file size)
• Videos (who created, description, image dimensions, file size, duration)

Yeah, you could write these out into four completely separate classes. The problem is, you're already going to have to write all those properties each and every time for every single class - and you're going to end up with code duplication along the way as functionality gets added.

Imagine you're now asked to add a few features:

• Checking to see whether the file size is beyond a certain threshold.
• Checking to see whether it's too high of resolution of video/picture.

If you had those four classes as four distinct entities? You're going to start having to code in multiple places.

But what happens if you use inheritance?

... look how the code only has to be written once, and the properties only have to be defined once. All Content Management files have to have a 'who created', a 'description', a 'file size', and a way to check whether that size is too great. So they're all defined at the base level. Down a level from there is the ImageFileInfo class, which adds a Dimensions property and a check whether those dimensions are too large. Finally, the Video (MovingImageFileInfo) doesn't rewrite the wheel - it takes all the stuff inside the ImageFileInfo class, and simply tacks on a durationInSeconds property.

• 2 $\begingroup$ Seems like there's a blurring of the lines for separation of concerns here. The file info (creator, size, and maybe description) are one thing, the info for image/video has nothing to do with the file, and should be a separate object that has-a file. The file is not the image, the file holds the image. $\endgroup$ –  Gypsy Spellweaver Commented May 4, 2018 at 16:38
• $\begingroup$ Indeed, perhaps ImageFileInfo ought to supply ImageInfo as a property rather than providing methods acting on the image data. Otherwise, I think this is a somewhat realistic example, though it could do with an example of a virtual function. $\endgroup$ –  Pharap Commented May 5, 2018 at 12:06
• $\begingroup$ Oh, Absolutely! In the real version of my code, a document consists of two objects: a Content class and an IndexCard - with the IndexCard containing metadata for the document itself, and the Content class containing the file (and data like its size, type, extension, etc.) I was just trying to simplify it down to a bite-sized example of how inheritance can be used well, and in a way that students wouldn't think of as "Eh, this is just theoretical stuff we'd never need to use." $\endgroup$ –  Kevin Commented May 7, 2018 at 13:49
• 2 $\begingroup$ Originally I upvoted this, but in hindsight I think this is a good case of where "composition over inheritance" should be applied. Virtual functions aren't being used, so I'm not convinced this is a good use of inheritance. I think it could be a good example if there was a clear use case for virtuality, but without that it seems that there's no reason to favour inheritance over composition. $\endgroup$ –  Pharap Commented Mar 26, 2021 at 21:09
• $\begingroup$ If you want to bring up all sorts of exciting issues around inheritance, add a SoundFileInfo class. Sound files have a duration but not dimensions: should MovingImageFileInfo inherit from both SoundFileInfo and ImageFileInfo (which brings up the diamond problem) or be its own thing (which leads to code duplication)? $\endgroup$ –  Mark Commented Feb 10, 2023 at 1:59

My coding school gave one particular (weeks-long) project that I felt nailed the concept of inheritance, and why it could be useful:

Simulating a circuit board with logic gates.

The framework of the exercise can be adjusted, but here's a short example:

A circuit board is composed of circuit inputs, logic gates and circuit outputs; each of these components has a variable number of input pins and output pins. The output pin of a component can be connected to the input pin of another. For instance, in the above circuit, there are three circuit inputs (A, B and C), and one circuit output (Z); the AND gate at the bottom has two input pins, and one output pin, connected to the input pin of the OR gate on the right. The goal of the exercise is to write a program that simulates a circuit board with the above rules; the program must e.g. parse a simple file describing the list of components, and how they're connected together; then parse the command line for commands such as setInput B true or updateCircuit or printOuput Y . (or give the students another framework if you don't want them to worry about parsing text) If a logic gate forms a loop, the "loop part" must be delayed until the next update. You must implement the following components: AND Gate OR Gate NOT Gate XOR Gate Multiplexer ... The circuits components must inherit from the following class: class CircuitComponent { public: virtual size_t getInputCount() const = 0; virtual void connectInput(size_t inputPin, const CircuitComponent* other, size_t outputPin) = 0; virtual void updateOutputsFromInputs() = 0; virtual size_t getOutputCount() const = 0; virtual bool getOutputValue(size_t outputPin) const = 0; };

There are several things that I like about this exercise:

It's as close to a real example as you can get.

It's, in my opinion; a use case where inheritance is the best solution; unlike other cases where some form of composition might be better suited.

It shows how a good base class can make your workflow easier; with the interface I gave, there is basically only one update model that can be implemented (updating the inputs, then the components connected to the inputs, then the components connected to these components, etc). It's also a good demonstration of expressivity through const-correctness.

It still has a few classic pitfalls of inheritance that most students will fall for, that you can easily point out. For instance, most students will implement circuit inputs and circuit outputs as children of the component class, and store them in one list/array with all other components, then use some convoluted dynamic_casting when they need to access the circuit's inputs/outputs. If they make that mistake, you can then point them towards a better solution, like storing inputs, logic gates and outputs in three different arrays, while still inheriting them from the same class, and they'll have learned from experience.

• $\begingroup$ While I like the idea, this only works if you actually understand logic gates. Thinking back to when I was taught programming in college, I don't think any of the class had ever heard the words "logic gate" (unless perhaps they played Minecraft). $\endgroup$ –  Pharap Commented Mar 26, 2021 at 21:11

Some commentary: What do you mean by "meaningful?" Are you looking for a program that does something useful? And what do you mean by useful? Do you need to have in-depth discussions of covariance and contravariance or just talk about the basics of inheritance? These are rhetorical questions but I think how you address these questions changes the parameters for a good answer.

Anyways, my suggestion is to look at inheritance in game engines. I think you can tailor some examples to cover your learning requirements. Depending on how much of a foundation you provide can give various degrees of a working product at the end of a semester. I'm not suggesting you build a game engine in a semester, but discuss some naive approaches and then look at real-world examples and then [some hands on project]. I think this has the added benefit of being of interest to at least a few students who found there way to a CS class by interest in creating video games (and you can provide a dash of realism on the difficulties in delivering a working game from scratch).

Two examples, as promised in the comments.

The Doom 3 source is available online and generally pleasant to read. Here are a few inheritance chains

You can find the source at https://github.com/dhewm/dhewm3/tree/master/neo/game .

A different kind of game is Cataclysm: Dark Days Ahead , a console/TUI game. The code is also a bit more "DIY" than the Doom 3 source. The player inheritance chain starts with two base classes, Creature and template <typename T> class visitable . Then the inheritance chain is

You can find the source online at https://github.com/CleverRaven/Cataclysm-DDA .

• $\begingroup$ @buffy e.g. the doom 3 source github.com/dhewm/dhewm3/tree/master/neo I'll try to pull out some inheritance chains later $\endgroup$ –  BurnsBA Commented May 1, 2018 at 20:31

I think showing examples from the Python language can be helpful.

Exception hierarchy :

BaseException +-- SystemExit +-- KeyboardInterrupt +-- GeneratorExit +-- Exception +-- StopIteration +-- StopAsyncIteration +-- ArithmeticError | +-- FloatingPointError | +-- OverflowError | +-- ZeroDivisionError +-- AssertionError +-- AttributeError +-- BufferError +-- EOFError +-- ImportError | +-- ModuleNotFoundError +-- LookupError | +-- IndexError | +-- KeyError +-- MemoryError +-- NameError | +-- UnboundLocalError +-- OSError | +-- BlockingIOError | +-- ChildProcessError | +-- ConnectionError | | +-- BrokenPipeError | | +-- ConnectionAbortedError | | +-- ConnectionRefusedError | | +-- ConnectionResetError | +-- FileExistsError | +-- FileNotFoundError | +-- InterruptedError | +-- IsADirectoryError | +-- NotADirectoryError | +-- PermissionError | +-- ProcessLookupError | +-- TimeoutError +-- ReferenceError +-- RuntimeError | +-- NotImplementedError | +-- RecursionError +-- SyntaxError | +-- IndentationError | +-- TabError +-- SystemError +-- TypeError +-- ValueError | +-- UnicodeError | +-- UnicodeDecodeError | +-- UnicodeEncodeError | +-- UnicodeTranslateError +-- Warning +-- DeprecationWarning +-- PendingDeprecationWarning +-- RuntimeWarning +-- SyntaxWarning +-- UserWarning +-- FutureWarning +-- ImportWarning +-- UnicodeWarning +-- BytesWarning +-- ResourceWarning

In my opinion, seeing a graphical representation like this makes everything much easier to understand, because it's a practical example, and it's easy to see that ZeroDivisionError would be a subclass of ArithmeticError . This example works for more languages, too, since Java has something similar.

An exercise could involve creating and extending your own Exception classes.

The linked documentation does a great job of describing what each class adds to its base class. Since computer science students should also be familiar with these mathematical "classes" of numbers and their various properties, this can be a useful example, depending on the age of the students.

There are plenty of mathematical concepts that can be used as an exercise for inheritance, so pick some that are simple enough for your class to work with and have them create a tree-style diagram of the inheritance.

• 1 $\begingroup$ Exceptions work differently to most class hierarchies - they are ontological and the type is important, whereas in most OO it's the behaviour that is important. They feel more like how you'd use types in functional languages for pattern matching than pure objects. $\endgroup$ –  Pete Kirkham Commented May 4, 2018 at 10:06

If the students are still needing real "objects" to connect metally with the concept of object you could resort to using transportation as a system. Another user, G. Ann - SonarSource Team , gave a good break down you could follow in answer to another question .

On the other hand, if you are looking for a more practical use-case, then you can use lists. There is the Node , which in its simplest form is nothing more than a data encapsulation, and the List which implements the process of accessing the nodes. The List and Node can both be inherited as you expand from array-based lists to linked lists, and into doubly linked lists. Then you can switch to stacks and queues, maybe even moving into binary, and n-ary, trees.

Kind of a meta answer:

• Pick any large, established, well-received Java library/API; especially one that ships with the regular open-source JDK. You will find a lot of examples of inheritance, conveniently displayed at the top of each "class" page in the Javadoc. Most of these should have been chosen by their authors with good reasons, and you certainly could do worse than use those as examples.
• I personally would rather avoid Person / Animal style examples as well; as you, I find many of those either far-fetched or useless insofar as they only show the bare minimum, staying shy of any obvious problems that might arise in real world settings. Most importantly, many of those I saw in the past would do better by using other structural patterns (like Composite ) instead of inheritance.
• While you're at it, you could teach your pupils about the fact that the kind of inheritance we have in, say, C++ or Java is only one kind of possible implementation; and that there can be (and are ) other solutions to whatever problem it is solving. For example, duck typing (e.g. ruby with its weird but utterly wonderful approach to the theme, google "ruby superclass" or "metaprogramming"), object-based class-less OOP (e.g. JavaScript no classes , how 'new' works ).

C# practical example:

Imagine you were making a super-awesome video game, and you needed to write a function that saves the game.

But where will all this data be saved? A simple text file? A binary file? An SQL database? A NoSQL database? Something else entirely?

Luckily, you don’t have to make the decision right now. No, the decision is configured by the user when the game is installed. So actually it’s not a lucky thing, because now you have to support all the options:

All nice and dandy. However, in this case there are only four if s. But what if we had thirty? Or fifty? Or fifty-three? And what if there are a whole bunch of nested ifs? The situation can easily become… (drumroll)… iffy .

And it gets worse: What if you’re writing code for other developers, and you want to allow them to add their very own ways of saving?

With inheritance, we eliminate the need for all these if s, and allow future programmers to add their own saving method:

Now, if new developers want to add their own way of saving, they can write a new class the implements Saver, and just pass it to the SaveTheGame method.

• 1 $\begingroup$ I don't see the need for the Saver class here, and when that is gone, there is no inheritance in that example. In statically typed languages Saver would be an interface and not a class and in Python (the language used by the OP) the Saver class simply doesn't make sense. Python programmers would just remove it. Duck-typing at work. $\endgroup$ –  BlackJack Commented May 2, 2018 at 17:03
• $\begingroup$ This doesn't save any code, it just moves it around. $\endgroup$ –  Stack Exchange Supports Israel Commented May 3, 2018 at 3:57
• $\begingroup$ @BlackJack Firstly, inheriting an interface is still inheritance. Secondly, one could argue that duck typing removes the need for any inheritance. Similarly, you could argue that having function objects renders inheritance redundant. As it happens, inheritance is typically implemented by what is effectively a structure full of function pointers. But none of that answers the OP's question. $\endgroup$ –  Pharap Commented Mar 26, 2021 at 21:21
• $\begingroup$ I recommend bolding that last line. The ability to add new saving strategies without needing to modify existing code is exactly why this is a good example of inheritance. This is also an excellent example to use for introducing the students to dependency injection, and an exaple of the strategy pattern (where the strategy here is how the data is saved). $\endgroup$ –  Pharap Commented Mar 26, 2021 at 21:24

Implement nested arithmetic expressions.

Let me start with what it can look like, and then I'll explain why it's a great example.

It starts very simple:

Then it slightly grows:

And yet a bit more:

And it can go on for quite a while.

Why is it a great example?

• it's small,
• it implements familiar objects,
• it is something useful (every calculator or interpreter has some code like this).

How can it be extended?

• add pretty printing (advanced flavor: with minimal number of parentheses),
• add variables (so that evaluate takes environment dict as argument),
• add more operations,
• add logical expressions.

Where is the inheritance?

I'd like to point that I didn't use Python's subclassing at any point here, and it was on purpose: Python's subclassing is mostly about implementation inheritance, and here it's not necessary at all. Of course, if you use type hints, you should define an interface, but only in that case. Python is generally duck-typed and there's not much point in pretending it's not. However, you can also add some shared implementation to this example.

Adding implementation inheritance

There is at least one thing that all kinds of expressions may easily share: caching . Example base class could look like this:

A few tweaks to expression classes, and basic caching is there.

Another idea to add common implementation would be listing free variables occuring in the expression (after adding variables ofc). First, make subclasses implement method subexpressions() (returning list of subexpressions, e.g. self.parts in case of sum). After that, implement method variables in Expression, and override it in Var/Variable (to return the single variable used there). The effect should be something like:

One problem with these examples is that the base class is more of a mixin than a real base. But I don't think you can do much better without going big. So, ultimately, you may want to go big.

Want really interesting inheritance? Go big, use a framework.

While little examples like above are good for understanding the basics, the most practical examples of implementation inheritance are big, all-inclusive classes provided by frameworks, like Django's views and forms . You may consider using them to show some practical uses of inheritance. While writing a Django¹ application is definitely an overkill, modifying one may be perfectly good task even on (relatively) early level.

If you prepare a working application that needs relatively small modification, like adding a view with different sorting, it may be a good hands-on experience. However, this is risky, and may be daunting experience if either students or exercise are not prepared well enough, so proceed with great care (if at all).

¹There's a number of frameworks with great examples, Django is just the one I'm familiar with.

When I want to give an example of how inheritance works, I always point to C#'s Stream class.

The Stream class is an abstraction of the idea of a data stream from which bytes can be taken or to which bytes can be stored. Its child classes include FileStream which represents the data of a file, MemoryStream which represents data in memory (RAM), BufferedStream which is an adaptor to provide an extra layer of data buffering, and CryptoStream which represents a layer of encryption.

It's a very abstract example, but it's a real world example that highlights how different implementations of the same interface can be incredibly useful. It demonstrates the use of virtual functions, abstraction, the dependency inversion principle and the liskov substitution principle .

Any Stream can be wrapped in a StreamReader , StreamWriter , BinaryReader or BinaryWriter to handle the ability to read/write data more complex than bytes. These are also good examples of the decorator pattern being used 'in the wild'. ( StreamReader and StreamWriter in turn inherit TextReader and TextWriter , which are themselves another good example.)

Part of the "teach OOP" problem is that OOP (and modularity, and top-down design, and variable-naming discipline, and consistent code layout, and...) is practically useful for large programs with a long life, and in the time allotted you write tiny throwaway programs.

Perhaps a way around that is reading (good!), hopefully modifying/extending, programs written in OOP style. Open source is a godsend...

I don't think inheritance is terribly important so I don't spend much time on it.

• First I let students define a Point class, which just contains two coordinate.
• Then they write a Rectangle class, where a rectangle (axi-parallel) is constructed from point/height/width.
• The rectangle class has methods such as area .
• Then write a Square class, constructed from only point/width.

They need to figure out

• How to let the square constructor use the rectangle one, and
• See for themselves that the square immediately has an area function, which it inherits.

And that's about it for inheritance in my class. I give them some pretty stiff programming projects, and none of those really need inheritance.

• $\begingroup$ If you'd keep nothing but first n last sentence you'd get not just my +1 but a bounty as well 😅. More seriously everyone seems to agree (almost) that all the famous inheritance egs are broken. But then hedge about saying that. (you come closest). So I guess the real question : When did the tide turn? And can you situate it in the mouths of some "big OO guy" like Stroustrup, B Meyer, Booch etc?? Closest I get is "Accelerated C++" saying «Forget all the fancy C++ . Just use STL. Write real significant programs to a flying start» $\endgroup$ –  Rushi Commented Feb 15, 2022 at 4:21
• $\begingroup$ I haven't been part of the C++ community long enough to have seen a tide turn. Inheritance definitely has its uses. In my field of scientific computing there are enough packages that use it. Maybe it only comes into play at a certain level of complexity. But yes, I really dislike the person/animal/whatever toy examples. From a taxonomical point of view they may make sense but not from a programming point where an object is a "packet of behaviors" as someone (you?) put it. $\endgroup$ –  Victor Eijkhout Commented Feb 15, 2022 at 5:48

I'm not sure why you don't like the person/employee/manager hierarchy; it is just an example for a whole class of object hierarchies which represent specializations of data with a common subset and are often stored in databases. Other examples would be non-human inventory (every physical item a company owns has a value and a location etc.), or financial assets (they all have some proof of ownership, a value, a date of acquisition etc.).

If you are looking for something which can be implemented and played with in a class I have two suggestions:

If there is a graphics library available, graphical objects in a 2-D or 3-D world which all have a position, can be transformed, displayed etc. form a nice hierarchy.

Because Python is good at parsing text, a calculator similar to a bc subset comes to mind which essentially processes a succession of potentially nested expressions, each of which has a value. The inheritance hierarchy would model the grammatical hierarchy of the language: subclasses of expression could be literal_value , simple_expression , variable etc.

• 2 $\begingroup$ The problem with person->employee->manager is that it can be difficult to evolve an Employee into a Manager. This is a frequent use case, but the methods (behaviors) open to a Manager are different from those of an Employee and certainly of the general Person. This is thinking of classes as a "classification" system, rather than way to define "bundles of behavior". It is the public methods (the behaviors) that make a class what it is. Likewise thinking of objects as bundles of data (rather than behaviors) leads to lots of poor designs. Make Manager a Trait of employee, not a subclass. $\endgroup$ –  Buffy Commented May 2, 2018 at 16:59
• 1 $\begingroup$ @Buffy Well, it appears to me that the problems you describe are inherent to the very concept of (true, as opposed to mere interface) inheritance. Paradigms have shifted away from this pattern towards composition for many reasons, yours among them, but these examples are what (true) inheritance is about, like it or not. If one wants to teach it, one has to teach these concepts together with the caveats. [As an aside, evolving an employee into a manger is relatively easy in a program, compared to the pesky reality...] $\endgroup$ –  Peter - Reinstate Monica Commented May 2, 2018 at 18:12
• 1 $\begingroup$ I disagree. I think they are just a consequence of shallow thought and poor design. However, if they are poorly taught the situation won't improve. Work for change. Bad design isn't compulsory. $\endgroup$ –  Buffy Commented May 2, 2018 at 18:15

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Oop using c++ – c++ programming inheritance based questions and answers.

Home » Computer Science Questions Answers for Written Exam » Object Oriented Programming using CPP Questions Answers for Written Exams and Interviews » OOP Using C++ – C++ Programming Inheritance based Questions and Answers

• Certainly! Here’s a list of 100 C++ programming inheritance-based questions for practicing inheritance concepts:

On this page

1. What is inheritance in C++?

Inheritance is a fundamental concept in object-oriented programming that allows a class to inherit properties (member variables and member functions) from another class. The class that inherits is called the “derived class” or “subclass,” and the class being inherited from is called the “base class” or “superclass.” Inheritance establishes a hierarchical relationship between classes, where the derived class inherits the characteristics of the base class.

2. What is the purpose of inheritance in object-oriented programming?

The purpose of inheritance in object-oriented programming is to promote code reuse and create a hierarchical structure of classes. It allows the derived class to inherit the properties and behaviors of the base class, reducing code duplication and improving maintainability. Inheritance also enables polymorphism, where objects of the derived class can be treated as objects of the base class, providing flexibility and extensibility in the design of software systems.

3. How do you declare a derived class in C++?

To declare a derived class in C++, you use the `class` keyword followed by the name of the derived class and the keyword `: public` followed by the base class from which it inherits. Here’s an example:

4. What is a base class in C++?

A base class in C++ is a class that serves as the foundation for derived classes. It contains common properties and behaviors that can be inherited by one or more derived classes. The base class provides the blueprint for creating objects, and the derived classes extend or specialize the base class by adding their unique properties and behaviors.

5. How do you define a base class in C++?

A base class in C++ is defined using the `class` keyword followed by the name of the base class. It can contain member variables, member functions, constructors, and destructors. Here’s an example:

6. What is single inheritance in C++?

Single inheritance in C++ is a type of inheritance where a derived class inherits from only one base class. It forms a simple hierarchical relationship between two classes, where the derived class inherits the properties of the single base class.

7. How do you implement single inheritance in C++?

Single inheritance in C++ is implemented by specifying the base class name after the colon (`:`) in the derived class declaration. Here’s an example:

8. What is multiple inheritance in C++?

Multiple inheritance in C++ is a type of inheritance where a derived class can inherit from multiple base classes. It allows a class to inherit properties and behaviors from more than one class simultaneously. With multiple inheritance, the derived class combines features from multiple base classes.

9. How do you implement multiple inheritance in C++?

Multiple inheritance in C++ is implemented by specifying multiple base class names separated by commas (`,`) after the colon (`:`) in the derived class declaration. Here’s an example:

10. What is multilevel inheritance in C++?

Multilevel inheritance in C++ is a type of inheritance where a derived class is derived from another derived class. It forms a hierarchical chain of classes, where each derived class inherits properties from its immediate base class, which in

turn can be derived from another base class.

11. How do you implement multilevel inheritance in C++?

Multilevel inheritance in C++ is implemented by specifying the base class name after the colon (`:`) in the derived class declaration. This process can be repeated to create a chain of derived classes. Here’s an example:

12. What is hierarchical inheritance in C++?

Hierarchical inheritance in C++ is a type of inheritance where multiple derived classes are derived from a single base class. It forms a hierarchical structure with a common base class and multiple classes derived from it.

13. How do you implement hierarchical inheritance in C++?

Hierarchical inheritance in C++ is implemented by specifying the base class name after the colon (`:`) in each derived class declaration. Here’s an example:

14. What is hybrid inheritance in C++?

Hybrid inheritance in C++ is a combination of multiple types of inheritance, such as single, multiple, multilevel, or hierarchical inheritance. It allows creating complex class hierarchies by combining different inheritance types.

15. How do you implement hybrid inheritance in C++?

Hybrid inheritance in C++ is implemented by combining different types of inheritance in a class hierarchy. It can involve using multiple base classes with different inheritance types, such as single, multiple, multilevel, or hierarchical inheritance.

16. What is the difference between public, private, and protected inheritance in C++?

In C++, the access specifiers (`public`, `private`, and `protected`) determine the visibility and accessibility of the inherited base class members in the derived class. The differences between these access specifiers are as follows:

– Public Inheritance: In public inheritance, the public members of the base class become public members of the derived class, and the protected members of the base class become protected members of the derived class. The private members of the base class are not accessible directly by the derived class.

– Private Inheritance: In private inheritance, all members of the base class become private members of the derived class. This means that both the public and protected members of the base class become private members in the derived class. The private members of the base class are not accessible directly by the derived class.

– Protected Inheritance: In protected inheritance, the public and protected members of the base class become protected members of the derived class. This means that the public members of the base class are accessible as protected members in the derived class. The private members of the base class are not accessible directly by the derived class.

17. How do you define the access specifiers in a derived class in C++?

The access specifiers (`public`, `private`, and `protected`) in a derived class can be defined before the base class name in the derived class declaration. By default, if no access specifier is specified, the access level is `private`. Here’s an example:

Replace `access_specifier` with `public`, `private`, or `protected` based on the desired access level.

18. How do you access base class members in a derived class in C++?

Base class members can be accessed in a derived class using the dot (`.`) operator or the scope resolution operator (`::`) followed by the base class name. The specific access depends on the access specifiers used. Here’s an example:

19. What is the difference between a derived class and a base class in C++?

In C++, a derived class is a class that inherits properties and behaviors from another class called the base class. The derived class extends or specializes the base class by adding its unique properties and behaviors. The key differences between a derived class and a base class are:

– A derived class inherits the members (variables and functions) of the base class, while the base class does not inherit from any other class. – The derived class can add additional members or modify the behavior of the inherited members, whereas the base class remains unchanged. – Objects of the derived class can be treated as objects of the base class, but objects of the base class cannot be treated as objects of the derived class. – The derived class forms a more specialized version of the base class and may have additional functionality or behavior.

20. How do you create an object of a derived class in C++?

To create an object of a derived class in C++, you can simply use the class name and call the constructor of the derived class. The constructor of the derived class implicitly calls the constructor of the base class. Here’s an example:

21. What is a constructor in a derived class in C++?

A constructor in a derived class is a special member function that is called when an object of the derived class is created. It is used to initialize the derived class object and its base class subobject. The derived class constructor can invoke the base class constructor to initialize the base class members.

22. How do you define and implement a constructor in a derived class in C++?

A constructor in a derived class is defined and implemented similar to a regular member function, but with the same name as the derived class. It can invoke the base class constructor using the constructor initializer list. Here’s an example:

In the example, the constructor of the derived class `DerivedClass` invokes the constructor of the base class `BaseClass` using the constructor initializer list `: BaseClass(value)`.

23. What is a destructor in a derived class in C++?

A destructor in a derived class is a special member function that is called when an object of the derived class is destroyed. It is used to perform cleanup tasks and deallocate resources used by the derived class and its base class.

24. How do you define and implement a destructor in a derived class in C++?

A destructor in a derived class is defined and implemented similar to a regular member function, but with the same name as the derived class preceded by a tilde (`~`). It can invoke the base class destructor implicitly to perform cleanup tasks. Here’s an example:

In the example, the destructor of the derived class `DerivedClass` automatically calls the destructor of the base class `BaseClass` as part of the cleanup process.

25. Can a derived class access private members of a base class in C++?

No, a derived class cannot access the private members of a base class directly. Private members are only accessible within the scope of the base class itself. However, the derived class can access the inherited private members indirectly through public or protected member functions of the base class.

26. Can a derived class override a base class member function in C++?

Yes, a derived class can override a base class member function in C++. Function overriding is the ability of a derived class to provide a different implementation for a virtual member function declared in the base class. The function signature (return type, name, and parameters) must match in the base and derived classes for successful overriding.

27. How do you override a base class member function in a derived class in C++?

To override a base class member function in a derived class, you need to declare the function with the same signature (return type, name, and parameters) as the base class member function. Additionally, you need to use the `override` keyword to indicate that the function is intended to override a virtual function from the base class. Here’s an example:

In the example, the `DerivedClass` overrides the `memberFunction` of the `BaseClass` by declaring a function with the same signature and using the `override` keyword.

28. Can a derived class add new member functions that are not present in the base class in C++?

Yes, a derived class can add new member functions that are not present in the base class. Derived classes can extend the functionality of the base class by adding new member functions specific to the derived class. These new member functions can be accessed only through objects of the derived class.

29. Can a derived class add new member variables that are not present in the base class in C++?

Yes, a derived class can add new member variables that are not present in the base class. Derived classes can have their unique member variables in addition to the inherited member variables from the base class. These new member variables can be accessed only through objects of the derived class.

30. Can a derived class have the same member variables as the base class in C++?

Yes, a derived class can have the same member variables as the base class. The derived class inherits the member variables from the base class, and it can also define its own member

variables. If the derived class defines a member variable with the same name as the base class, it hides the base class member variable. However, the base class member variable can still be accessed using the scope resolution operator (`::`) with the base class name.

31. What is function hiding in C++?

Answer: Function hiding in C++ occurs when a derived class defines a function with the same name as a function in the base class, but the functions have different signatures. The derived class function “hides” the base class function, and the base class function becomes inaccessible through objects of the derived class.

32. How do you hide a base class function in a derived class in C++?

Answer: To hide a base class function in a derived class, you can define a function in the derived class with the same name but a different signature than the base class function. This will cause the base class function to be hidden in the derived class. You can use the `using` keyword to bring the hidden base class function into the derived class scope if needed.

33. What is the difference between function hiding and function overriding in C++?

Answer: In C++, function hiding and function overriding are two different concepts:

– Function hiding occurs when a derived class defines a function with the same name as a function in the base class but with a different signature. The base class function is hidden and not accessible through objects of the derived class. Function hiding is static and determined at compile-time.

– Function overriding occurs when a derived class provides a different implementation for a virtual function declared in the base class. The function signature must be the same in both the base and derived classes. Function overriding is dynamic and determined at runtime based on the actual type of the object.

34. What is a virtual base class in C++?

Answer: A virtual base class in C++ is a base class that is declared as virtual in a class hierarchy. When a class is derived from a virtual base class, the virtual base class subobject is shared among all the derived classes. This ensures that there is only one instance of the virtual base class within the complete object hierarchy.

35. How do you declare a virtual base class in C++?

Answer: To declare a virtual base class in C++, you add the `virtual` keyword before the base class name in the derived class declaration. For example:

In this example, the `virtual` keyword before the base class `BaseClass` indicates that it is a virtual base class.

36. What is the purpose of a virtual base class in C++?

Answer: The purpose of a virtual base class in C++ is to avoid the problems associated with multiple inheritance, such as the “diamond problem.” By declaring a base class as virtual, it ensures that only a single instance of that base class exists in the complete object hierarchy, even if it is inherited by multiple paths. This prevents duplicate copies of the virtual base class and ensures proper initialization and sharing of common data.

37. What is the diamond problem in multiple inheritance in C++?

Answer: The diamond problem is a name collision issue that arises in multiple inheritance when a class inherits from two or more classes that share a common base class. It leads to ambiguity in accessing the members of the common base class, as there are multiple paths to reach them. This can result in compilation errors or unexpected behavior.

38. How do you resolve the diamond problem in multiple inheritance in C++?

Answer: The diamond problem in multiple inheritance can be resolved in C++ by using virtual inheritance. By declaring the common base class as a virtual base class in the derived classes, it ensures that only a single instance of the base class exists in the complete object hierarchy. This resolves the ambiguity and allows proper access to the common base class members.

39. What is an abstract base class in C++?

Answer: An abstract base class in C++ is a class that is designed to be used as a base

class and cannot be instantiated on its own. It is often used to define a common interface or behavior that derived classes must implement. An abstract base class typically contains one or more pure virtual functions, making it an abstract class.

40. How do you define and use an abstract base class in C++?

Answer: To define an abstract base class in C++, you declare at least one pure virtual function in the class. A pure virtual function is declared using the `virtual` keyword and assigning it a value of `0` (zero) as its implementation. For example:

To use an abstract base class, you derive a concrete class from it and provide implementations for all the pure virtual functions. The derived class becomes a concrete class and can be instantiated.

41. Can you create objects of an abstract base class in C++?

Answer: No, you cannot create objects of an abstract base class in C++. An abstract base class is designed to be used as a base class and cannot be instantiated on its own because it contains pure virtual functions that have no implementation. However, you can create objects of derived classes that inherit from the abstract base class.

42. What is a pure virtual function in C++?

Answer: A pure virtual function in C++ is a virtual function that is declared in a base class but has no implementation. It is declared using the `virtual` keyword and assigning it a value of `0` (zero) as its implementation. A pure virtual function serves as a placeholder that derived classes must override and provide an implementation for.

43. How do you declare and define a pure virtual function in C++?

Answer: To declare a pure virtual function in C++, you include the `virtual` keyword and assign it a value of `0` (zero) as its implementation. For example:

The pure virtual function has no implementation in the base class itself. It must be overridden and defined in the derived classes.

44. Can a pure virtual function have a definition in C++?

Answer: No, a pure virtual function cannot have a definition in C++. It is meant to be overridden and implemented in derived classes. However, it is possible to provide a default implementation for a pure virtual function by defining a non-pure virtual function with the same name in the base class. Derived classes can choose to override this non-pure virtual function or use the default implementation.

45. What is the difference between an abstract base class and a concrete base class in C++?

Answer: In C++, an abstract base class is a class that is designed to be used as a base class and cannot be instantiated on its own. It typically contains one or more pure virtual functions. A concrete base class, on the other hand, is a regular class that can be instantiated and used on its own, without necessarily having any pure virtual functions.

46. What is a constructor initializer list in a derived class in C++?

Answer: A constructor initializer list in a derived class in C++ is used to invoke the base class constructor and initialize the base class subobject within the derived class constructor. It specifies the arguments to be passed to the base class constructor and any additional initialization for member variables in the derived class.

47. How do you use a constructor initializer list in a derived class in C++?

Answer: To use a constructor initializer list in a derived class in C++, you include the base class name followed by parentheses and pass the necessary arguments to the base class constructor. For example:

In this example, the constructor initializer list `: BaseClass(arg1)` initializes the base class using the `arg1` argument, and `memberVariable(arg2)` initializes the member variable `memberVariable` with the `arg2` argument.

48. What is the purpose of a constructor initializer list in a derived class in C++?

Answer: The purpose of a constructor initializer list in a derived class in C++ is to ensure that the base class constructor is called with the appropriate arguments and that the base class subobject is properly initialized before the derived class constructor body is executed. It allows you to initialize the base class and member variables in a concise and efficient manner.

49. What is a protected access specifier in C++?

Answer: In C++, the protected access specifier defines the access level for class members that are accessible within the class itself and its derived classes. Protected members are not accessible outside the class hierarchy but can be accessed by derived classes.

50. How do you use the protected access specifier in a derived class in C++?

Answer: To use the protected access specifier in a derived class in C++, you declare the desired member variables or functions with the `protected` keyword within the base class. These protected members can then be accessed directly by the derived class, just like private members, but are also accessible by other derived classes.

51. What is the difference between public and protected inheritance in C++?

Answer: In C++, public inheritance and protected inheritance are different ways of specifying the access level for inherited members:

– Public inheritance (`public` keyword) preserves the access levels of base class members in the derived class. Public members of the base class remain public in the derived class, protected members become protected, and private members are inaccessible.

– Protected inheritance (`protected` keyword) changes the access level of all members inherited from the base class to protected in the derived class. Public and protected members of the base class become protected in the derived class, while private members remain inaccessible.

52. What is the difference between protected and private inheritance in C++?

Answer: In C++, protected inheritance and private inheritance are similar in that they both change the access level of inherited members:

– Private inheritance (`private` keyword) changes the access level of all members inherited from the base class to private in the derived class. Both public and protected members of the base class become private in the derived class, and private members are inaccessible.

53. What is the use of the ‘using’ keyword in C++ inheritance?

Answer: The ‘using’ keyword in C++ inheritance is used to bring base class member functions or variables into the scope of the derived class. It allows the derived class to access and use the base class members as if they were its own.

54. How do you use the ‘using’ keyword to bring base class member functions into the derived class in C++?

Answer: To use the ‘using’ keyword to bring base class member functions into the derived class in C++, you include a ‘using’ declaration in the derived class for the desired base class member function. For example:

In this example, the ‘using’ declaration ‘using Base::baseFunction;’ brings the ‘baseFunction’ from the base class ‘Base’ into the scope of the derived class

‘Derived’.

55. What is the scope resolution operator (::) used for in C++ inheritance?

Answer: The scope resolution operator (::) in C++ inheritance is used to explicitly specify the scope from which a particular member function or variable is accessed. It can be used to access members of the base class from within the derived class, or to access members of the derived class from outside its scope.

56. How do you access base class members using the scope resolution operator in C++ inheritance?

Answer: To access base class members using the scope resolution operator in C++ inheritance, you specify the name of the base class followed by the scope resolution operator (::) and the name of the member. For example:

In this example, ‘Base::baseFunction()’ and ‘Base::baseVariable’ access the base class member function and member variable, respectively, from within the derived class ‘Derived’.

57. How do you access derived class members using the scope resolution operator in C++ inheritance?

Answer: Since derived class members are accessible within the derived class itself, there is no need to use the scope resolution operator (::) to access them from within the derived class. However, you can use the scope resolution operator to access derived class members from outside the derived class. For example:

In this example, ‘derivedObject::derivedVariable’ accesses the member variable ‘derivedVariable’ of the derived class ‘Derived’ from outside its scope.

58. What is a friend class in C++ inheritance?

Answer: A friend class in C++ inheritance is a class that is granted access to the private and protected members of another class. A friend class can access the private and protected members of the class it is declared as a friend of, even though it is not derived from that class.

59. How do you declare a friend class in C++ inheritance?

Answer: To declare a friend class in C++ inheritance, you include a ‘friend’ declaration inside the class that you want to grant access to. For example:

In this example, ‘FriendClass’ is declared as a friend class of ‘MyClass’, granting it access to the private and protected members of ‘MyClass’.

60. What is the difference between a friend class and a base class in C++ inheritance?

Answer: In C++ inheritance, a friend class and a base class are different concepts:

– A friend class is a class that is granted access to the private and protected members of another class. It is not necessarily related through inheritance but is explicitly declared as a friend of the class.

– A base class, on the other hand, is a class from which another class (derived class) is derived. The derived class inherits the members and properties of the base class, including public, protected, and accessible private members.

61. What is a derived class constructor in C++ inheritance?

Answer: A derived class constructor is a special member function in a derived class that is responsible for initializing the derived class objects. It is called when an object of the derived class is created and is used to initialize the data members inherited from the base class as well as the additional data members specific to the derived class.

62. How do you define and implement a derived class constructor in C++ inheritance?

Answer: To define and implement a derived class constructor in C++ inheritance, you can use the constructor initializer list to initialize the base class subobject and specify any additional initialization steps for the derived class. Here’s an example:

63. What is the order of execution of base class and derived class constructors in C++ inheritance?

Answer: In C++ inheritance, the base class constructor is executed before the derived class constructor. This ensures that the base class subobject is properly initialized before any initialization specific to the derived class takes place. The order of execution is from the topmost base class to the most derived class.

64. What is a derived class destructor in C++ inheritance?

Answer: A derived class destructor is a special member function in a derived class that is responsible for cleaning up the resources allocated by the derived class objects. It is called when an object of the derived class goes out of scope or is explicitly deleted and is used to release the resources held by the derived class and its base class.

65. How do you define and implement a derived class destructor in C++ inheritance?

Answer: To define and implement a derived class destructor in C++ inheritance, you can simply provide the destructor definition within the derived class. The destructor will automatically call the base class destructor to ensure proper cleanup of resources. Here’s an example:

66. What is the order of execution of derived class and base class destructors in C++ inheritance?

Answer: In C++ inheritance, the derived class destructor is executed before the base class destructor. This ensures that the cleanup operations specific to the derived class are performed before the base class cleanup. The order of execution is from the most derived class to the topmost base class.

67. What is the difference between a derived class constructor and a derived class destructor in C++ inheritance?

Answer: The main difference between a derived class constructor and a derived class destructor in C++ inheritance is their purpose and functionality.

– Constructor: A derived class constructor is responsible for initializing the derived class objects, including initializing the base class subobject and any additional data members specific to the derived class. It is called when an object of the derived class is created. – Destructor: A derived class destructor is responsible for cleaning up the resources allocated by the derived class objects, including releasing the resources held by the derived class and its base class. It is called when an object of the derived class goes out of scope or is explicitly deleted.

68. What is a protected constructor in C++ inheritance?

Answer: A protected constructor in C++ inheritance is a constructor that is accessible within the derived class and its derived classes but not accessible outside the class hierarchy. It allows derived classes to invoke the constructor for initialization purposes, but prevents direct construction of

objects of the base or derived classes from outside the class hierarchy.

69. How do you declare a protected constructor in C++ inheritance?

Answer: To declare a protected constructor in C++ inheritance, you can use the `protected` access specifier before the constructor declaration within the class. Here’s an example:

70. What is the use of a protected constructor in C++ inheritance?

Answer: The use of a protected constructor in C++ inheritance is to enforce encapsulation and control the access to object creation within the class hierarchy. By declaring a constructor as protected, it allows derived classes to access and invoke the constructor for initialization, but restricts direct construction of objects of the base or derived classes from outside the class hierarchy.

71. What is a static member in a derived class in C++ inheritance?

Answer: A static member in a derived class in C++ inheritance is a member that belongs to the class itself rather than to the individual objects of the class. It is shared among all the objects of the derived class and its derived classes, as well as the base class. Static members are declared using the `static` keyword and can be accessed without creating an object of the class.

72. How do you declare and define a static member in a derived class in C++ inheritance?

Answer: To declare and define a static member in a derived class in C++ inheritance, you can use the `static` keyword in the class declaration and provide the definition outside the class. Here’s an example:

73. How do you access a static member of a base class in a derived class in C++ inheritance?

Answer: A static member of a base class can be accessed in a derived class using the scope resolution operator `::` along with the base class name. Here’s an example:

74. How do you access a static member of a derived class in C++ inheritance?

Answer: A static member of a derived class can be accessed using the class name itself, without the need for an object. Here’s an example:

75. What is a virtual destructor in C++ inheritance?

Answer: A virtual destructor in C++ inheritance is a destructor declared in the base class as virtual. It allows proper destruction of derived class objects through a base class pointer or reference. When a derived class object is deleted through a base class pointer or reference, the appropriate derived class destructor is invoked along with the base class destructor.

76. How do you declare and define a virtual destructor in C++ inheritance?

Answer: To declare and define a virtual destructor in C++ inheritance, you can add the `virtual` keyword before the destructor declaration in the base class. Here’s an example:

77. What is the purpose of a virtual destructor in C++ inheritance?

Answer: The purpose of a virtual destructor in C++ inheritance is to ensure proper destruction of derived class objects when they are deleted through a base class pointer or reference. Without a virtual destructor, only the base class destructor would be called, resulting in potential memory leaks or undefined behavior. A virtual destructor allows the appropriate derived class destructor to be invoked along with the base class destructor during object destruction.

78. What is an object pointer in C++ inheritance?

Answer: An object pointer in C++ inheritance is a pointer that can hold the memory address of an object of a base class or a derived class. It allows accessing the members and invoking the member functions of the object through the pointer.

79. How do you declare and initialize an object pointer in C++ inheritance?

Answer: To declare and initialize an object pointer in C++ inheritance, you can declare a pointer of the appropriate class type and assign it the address of the object using the address-of operator `&`. Here’s an example:

80. How do you access base class members using an object pointer in C++ inheritance?

Answer: Base class members can be accessed using an object pointer in C++ inheritance by using the arrow operator `->` along with the pointer name. Here’s an example:

81. How do you access derived class members using an object pointer in C++ inheritance?

Answer: Derived class members can be accessed using an object pointer in C++ inheritance by first casting the pointer to the appropriate derived class type using the `static_cast` or `dynamic_cast` and then using the arrow operator `->` along with the pointer name. Here’s an example:

82. What is a dynamic cast in C++ inheritance?

Answer: A dynamic cast in C++ inheritance is a type of cast used to safely convert pointers or references of a base class to pointers or references of a derived class at runtime. It performs a runtime check to ensure the validity of the cast and returns a null pointer if the cast fails.

83. How do you perform a dynamic cast in C++ inheritance?

Answer: To perform a dynamic cast in C++ inheritance, you can use the `dynamic_cast` operator followed

by the target type enclosed in parentheses. Here’s an example:

84. What is the purpose of a dynamic cast in C++ inheritance?

Answer: The purpose of a dynamic cast in C++ inheritance is to safely convert pointers or references of a base class to pointers or references of a derived class at runtime. It allows runtime type checking to ensure the validity of the cast and provides a way to access derived class members when working

with polymorphic objects.

85. What is a static cast in C++ inheritance?

Answer: A static cast in C++ inheritance is a type of cast used to perform simple conversions between related types, such as casting a pointer or reference of a base class to a pointer or reference of a derived class. It is resolved at compile-time and does not perform any runtime checks.

86. How do you perform a static cast in C++ inheritance?

Answer: To perform a static cast in C++ inheritance, you can use the `static_cast` operator followed by the target type enclosed in parentheses. Here’s an example:

87. What is the purpose of a static cast in C++ inheritance?

Answer: The purpose of a static cast in C++ inheritance is to perform simple conversions between related types, such as casting a pointer or reference of a base class to a pointer or reference of a derived class. It is useful when you know the types involved and want to perform explicit type conversion at compile-time.

88. What is an upcast in C++ inheritance?

Answer: An upcast in C++ inheritance is a type of cast that converts a pointer or reference of a derived class to a pointer or reference of its base class. It is a safe and implicit conversion, as the derived class is guaranteed to have all the members and functionality of the base class.

89. How do you perform an upcast in C++ inheritance?

Answer: An upcast in C++ inheritance is automatically performed when assigning a pointer or reference of a derived class to a pointer or reference of its base class. No explicit cast is required. Here’s an example:

90. What is the purpose of an upcast in C++ inheritance?

Answer: The purpose of an upcast in C++ inheritance is to treat a derived class object as an object of its base class. It allows accessing the base class members and functionality of the derived class object through a base class pointer or reference.

91. What is a downcast in C++ inheritance?

Answer: A downcast in C++ inheritance is a type of cast that converts a pointer or reference of a base class to a pointer or reference of a derived class. It is a potentially unsafe conversion, as the base class may not have the same members and functionality as the derived class.

92. How do you perform a downcast in C++ inheritance?

Answer: To perform a downcast in C++ inheritance, you can use either a `static_cast` or a `dynamic_cast` operator. However, it is generally recommended to use `dynamic_cast` for downcasting, as it performs a runtime check to ensure the validity of the cast. Here’s an example:

93. What is the purpose of a downcast in C++ inheritance?

Answer: The purpose of a downcast in C++ inheritance is to explicitly convert a pointer or reference of a base class to a pointer or reference of a derived class. It allows accessing the members and functionality specific to the derived class when necessary. However, downcasting should be used with caution and preferably with runtime type checking to ensure

the validity of the cast.

94. What is a pure virtual destructor in C++ inheritance?

Answer: A pure virtual destructor in C++ inheritance is a destructor declared as pure virtual in the base class. It is declared using the `virtual` keyword and assigning it the value `0` in the base class. A class with a pure virtual destructor is considered an abstract class and cannot be instantiated.

95. How do you declare and define a pure virtual destructor in C++ inheritance?

Answer: To declare and define a pure virtual destructor in C++ inheritance, you can add the `virtual` keyword before the destructor declaration in the base class and assign it the value `0`. Here’s an example:

96. Can a pure virtual destructor have a definition in C++ inheritance?

Answer: Yes, a pure virtual destructor can have a definition in C++ inheritance. The definition is provided outside the class similar to other member functions. The pure virtual destructor in the base class forces the derived classes to provide their own definitions for the destructor.

97. What is an abstract derived class in C++ inheritance?

Answer: An abstract derived class in C++ inheritance is a class that inherits from an abstract base class and has not provided definitions for all the pure virtual functions inherited from the base class. An abstract derived class is also considered an abstract class and cannot be instantiated.

98. How do you define and use an abstract derived class in C++ inheritance?

Answer: To define and use an abstract derived class in C++ inheritance, you can inherit from an abstract base class and provide definitions for all the pure virtual functions inherited from the base class. The derived class can then be used to create objects and invoke its member functions.

99. Can you create objects of an abstract derived class in C++ inheritance?

Answer: No, you cannot create objects of an abstract derived class in C++ inheritance. An abstract derived class is an incomplete class that has not provided definitions for all the pure virtual functions inherited from the base class. It is meant to be used as a base for further derived classes and cannot be instantiated.

100. What is the difference between an abstract derived class and a concrete derived class?

Answer: The difference between an abstract derived class and a concrete derived class lies in the level of completeness and the ability to instantiate objects.

– An abstract derived class is a class that inherits from an abstract base class and has not provided definitions for all the pure virtual functions inherited from the base class. It is an incomplete class and cannot be instantiated. It is used as a base for further derived classes that provide implementations for the pure virtual functions.

– A concrete derived class, on the other hand, is a class that inherits from a base class and provides definitions for all the inherited pure virtual functions. It is a complete class that can be instantiated and used to create objects. It adds specific functionality to the base class and can be further extended by additional derived classes.

In summary, an abstract derived class is incomplete and cannot be instantiated, while a concrete derived class is complete and can be instantiated.

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C++ Tutorial

C++ functions, c++ classes, c++ reference, c++ examples, c++ inheritance, inheritance.

In C++, it is possible to inherit attributes and methods from one class to another. We group the "inheritance concept" into two categories:

• derived class (child) - the class that inherits from another class
• base class (parent) - the class being inherited from

To inherit from a class, use the : symbol.

In the example below, the Car class (child) inherits the attributes and methods from the Vehicle class (parent):

Why And When To Use "Inheritance"?

- It is useful for code reusability: reuse attributes and methods of an existing class when you create a new class.

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• Getting Started With C++
• Your First C++ Program
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C++ Fundamentals

• C++ Keywords and Identifiers
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• C++ Data Types
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• C++ Basic Input/Output
• C++ Operators

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• C++ Relational and Logical Operators
• C++ if, if...else and Nested if...else
• C++ for Loop
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• C++ break Statement
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• C++ Ternary Operator
• C++ Functions
• C++ Programming Default Arguments
• C++ Function Overloading
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• C++ Array to Function
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• C++ Pointers
• C++ Pointers and Arrays
• C++ References: Using Pointers
• C++ Call by Reference: Using pointers
• C++ Memory Management: new and delete

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• C++ Structures
• C++ Structure and Function
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• C++ Enumeration

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• C++ Classes and Objects
• C++ Constructors
• C++ Constructor Overloading
• C++ Destructors
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• C++ friend Function and friend Classes

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C++ Inheritance

C++ Public, Protected and Private Inheritance

• C++ Multiple, Multilevel and Hierarchical Inheritance
• C++ Function Overriding
• C++ Virtual Functions

C++ Abstract Class and Pure Virtual Function

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• C++ Standard Template Library
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• C++ Multimap
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C++ Multiple, Multilevel, Hierarchical and Virtual Inheritance

Inheritance is one of the core features of an object-oriented programming language. It allows software developers to derive a new class from the existing class. The derived class inherits the features of the base class (existing class).

There are various models of inheritance in C++ programming.

• C++ Multilevel Inheritance

In C++ programming, not only can you derive a class from the base class but you can also derive a class from the derived class. This form of inheritance is known as multilevel inheritance.

Here, class B is derived from the base class A and the class C is derived from the derived class B .

• Example 1: C++ Multilevel Inheritance

In this program, class C is derived from class B (which is derived from base class A ).

The obj object of class C is defined in the main() function.

When the display() function is called, display() in class A is executed. It's because there is no display() function in class C and class B .

The compiler first looks for the display() function in class C . Since the function doesn't exist there, it looks for the function in class B (as C is derived from B ).

The function also doesn't exist in class B , so the compiler looks for it in class A (as B is derived from A ).

If display() function exists in C , the compiler overrides display() of class A (because of member function overriding ).

• C++ Multiple Inheritance

In C++ programming, a class can be derived from more than one parent. For example, A class Bat is derived from base classes Mammal and WingedAnimal . It makes sense because bat is a mammal as well as a winged animal.

• Example 2: Multiple Inheritance in C++ Programming
• Ambiguity in Multiple Inheritance

The most obvious problem with multiple inheritance occurs during function overriding.

Suppose two base classes have the same function which is not overridden in the derived class.

If you try to call the function using the object of the derived class, the compiler shows error. It's because the compiler doesn't know which function to call. For example,

This problem can be solved using the scope resolution function to specify which function to class either base1 or base2 .

• C++ Hierarchical Inheritance

If more than one class is inherited from the base class, it's known as hierarchical inheritance . In hierarchical inheritance, all features that are common in child classes are included in the base class.

For example, Physics, Chemistry, Biology are derived from Science class. Similarly, Dog, Cat, Horse are derived from Animal class.

Syntax of Hierarchical Inheritance

• Example 3: Hierarchical Inheritance in C++ Programming

Here, both the Dog and Cat classes are derived from the Animal class. As such, both the derived classes can access the info() function belonging to the Animal class.

• C++ Virtual Inheritance

Virtual inheritance is a C++ technique that makes sure that the grandchild derived classes inherit only one copy of a base class's member variables.

Let's consider the following class hierarchy.

Here, when Bat inherits from multiple classes; Mammal and WingedAnimal having the same base class; Animal , it may inherit multiple instances of the base class. This is known as the diamond problem.

We can avoid this problem using virtual inheritance.

Here, Derived1 and Derived2 both inherit from Base virtually, ensuring that Derived3 will have only one set of Base member variables, even though it inherits from both Derived1 and Derived2 .

• Example 4: Virtual Inheritance

In this example, the Bat class is derived from both WingedAnimal and Mammal , which are in turn derived from Animal using virtual inheritance.

This ensures that only one Animal base class constructor is called when an instance of Bat is created and the species_name is set to "Bat" .

Note : In the above program, if the virtual keyword was not used, the Bat class would inherit multiple copies of the member variable of the Animal class. This would result in an error.

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• Introduction

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Top 10 Interview Questions for C++ Developers

The success of your software projects hinges on hiring skilled C++ developers who can navigate the language’s intricacies and leverage its powerful features. Conducting thorough interviews is essential to identify candidates with the necessary expertise and problem-solving abilities. In this article, we present the top 10 interview questions for C++ developers, complete with explanations and assessment tips. These questions will help you discern the most qualified candidates, ensuring your team has the talent needed to drive your projects forward and achieve exceptional results.

1. What are the key features of C++?

Why Ask This? Understanding the fundamental features of C++ is essential for any developer. This question tests the candidate’s basic knowledge of the language.

What to Look For:

• Mention of object-oriented programming principles (inheritance, encapsulation, polymorphism).
• Discussion of templates and the Standard Template Library (STL) .
• Knowledge of memory management and pointers.
• Awareness of multiple inheritance and operator overloading.

Sample Answer: “C++ is an object-oriented programming language that supports classes and objects, inheritance, polymorphism, and encapsulation. It also offers templates and the Standard Template Library (STL) for data structures and algorithms. C++ provides low-level memory manipulation capabilities through pointers and allows multiple inheritance and operator overloading.”

2. How does C++ differ from C?

Why Ask This? This question assesses the candidate’s understanding of the evolution from C to C++ and their knowledge of the added features and improvements in C++.

• Awareness of object-oriented features added in C++.
• Discussion of stronger type checking and function overloading.
• Mention of the Standard Template Library (STL).
• Knowledge of namespaces and exception handling.

Sample Answer: “C++ builds on C by adding object-oriented features such as classes and objects. It also supports function overloading, stronger type checking, and the Standard Template Library (STL) for generic programming. C++ introduces namespaces to avoid naming conflicts and provides exception handling for better error management.”

3. Can you explain the concept of RAII (Resource Acquisition Is Initialization)?

Why Ask This? RAII is a key concept in C++ for managing resources. This question tests the candidate’s understanding of resource management and their ability to write robust C++ code.

• Clear explanation of RAII and its principles.
• Examples of how RAII is used in practice.
• Understanding of constructors and destructors.

Sample Answer: “RAII is a programming idiom used in C++ where resource allocation is tied to object lifetime. Resources such as memory, file handles, and network connections are acquired in the constructor and released in the destructor. This ensures that resources are properly cleaned up when the object goes out of scope, reducing the risk of resource leaks. For example, the std::unique_ptr and std::shared_ptr classes in C++ use RAII to manage dynamic memory.”

4. What are smart pointers, and how do they differ from regular pointers?

Why Ask This? Smart pointers are a critical feature in modern C++ for managing dynamic memory. This question evaluates the candidate’s familiarity with smart pointers and their benefits.

• Explanation of different types of smart pointers (std::unique_ptr, std::shared_ptr, std::weak_ptr).
• Comparison with regular pointers.
• Discussion of automatic memory management and reference counting.

Sample Answer: “Smart pointers in C++ are template classes that manage dynamic memory automatically. Unlike regular pointers, smart pointers ensure that memory is released when it is no longer needed. std::unique_ptr provides exclusive ownership, meaning only one smart pointer can own the object at a time. std::shared_ptr allows multiple smart pointers to share ownership of an object, using reference counting to manage the lifetime of the object. std::weak_ptr is used to avoid circular references with std::shared_ptr by providing a non-owning reference.”

5. What is the difference between deep copy and shallow copy?

Why Ask This? Understanding deep and shallow copies is crucial for managing resources and avoiding bugs in C++ programs. This question tests the candidate’s knowledge of copy semantics.

• Clear distinction between deep and shallow copies.
• Examples of when to use each type.
• Understanding of copy constructors and assignment operators.

Sample Answer: “A shallow copy copies the object’s pointer values, meaning both the original and the copy share the same memory address. This can lead to issues if one object modifies the shared resource. A deep copy, on the other hand, creates a copy of the object’s dynamic memory, ensuring that the original and the copy are independent. Deep copies are implemented using copy constructors and assignment operators to duplicate the dynamically allocated resources.”

6. How do you handle exceptions in C++?

Why Ask This? Exception handling is vital for writing robust and maintainable code. This question assesses the candidate’s understanding of exception handling mechanisms in C++.

• Explanation of try-catch blocks.
• Discussion of standard exceptions and custom exceptions.
• Knowledge of exception safety and best practices.

Sample Answer: “Exception handling in C++ is done using try-catch blocks. Code that may throw an exception is placed inside a try block, and the catch blocks handle specific exceptions. C++ provides standard exceptions like std::exception, std::runtime_error, and std::out_of_range. Developers can also define custom exceptions by inheriting from std::exception. It’s important to write exception-safe code, ensuring that resources are properly released even when an exception occurs. Using RAII and smart pointers helps achieve this.”

7. What is the purpose of the virtual keyword in C++?

Why Ask This? The virtual keyword is essential for implementing polymorphism in C++. This question evaluates the candidate’s understanding of virtual functions and inheritance.

• Explanation of virtual functions and their role in polymorphism.
• Understanding of base and derived classes.
• Knowledge of pure virtual functions and abstract classes.

Sample Answer: “The virtual keyword in C++ is used to declare virtual functions in a base class, allowing derived classes to override them. Virtual functions enable polymorphism, where a base class pointer or reference can call the overridden function in a derived class. A pure virtual function, declared with = 0, makes a class abstract, meaning it cannot be instantiated and must be inherited. This is useful for defining interfaces in C++.”

8. Can you explain the concept of move semantics in C++11?

Why Ask This? Move semantics introduced in C++11 optimize resource management and performance. This question tests the candidate’s knowledge of move semantics and related features.

• Explanation of move constructors and move assignment operators.
• Discussion of rvalue references and std::move.
• Examples of scenarios where move semantics improve performance.

Sample Answer: “Move semantics in C++11 allow resources to be transferred from one object to another without copying. This is done using move constructors and move assignment operators, which take an rvalue reference (&&). The std::move function casts an lvalue to an rvalue, enabling the use of move semantics. Move semantics improve performance by eliminating unnecessary deep copies, especially in classes managing dynamic memory or other resources.”

9. What is a lambda expression, and how is it used in C++?

Why Ask This? Lambda expressions are a powerful feature introduced in C++11 for writing inline functions. This question evaluates the candidate’s understanding of lambdas and their applications.

• Explanation of the syntax and components of a lambda expression.
• Examples of using lambdas in algorithms and event handling.
• Discussion of capture lists and lambda closures.

Sample Answer: “A lambda expression in C++ is an anonymous function that can be defined inline. The syntax includes a capture list, parameter list, and function body. Lambdas are useful for short, local functions, often used with STL algorithms like std::for_each or std::sort. The capture list allows lambdas to access variables from the surrounding scope. For example, [&](int x) { return x * 2; } defines a lambda that multiplies its input by 2, capturing variables by reference.”

10. How do you manage large projects in C++?

Why Ask This? Managing large projects requires good practices in code organization and build management. This question tests the candidate’s experience with large-scale C++ development.

• Knowledge of modularization and code organization.
• Use of build systems like CMake.
• Experience with version control and continuous integration.

Sample Answer: “Managing large projects in C++ involves modularizing code into smaller, manageable components using classes, namespaces, and separate header and source files. Build systems like CMake help automate the build process and manage dependencies. Version control systems like Git are essential for tracking changes and collaborating with other developers. Continuous integration tools like Jenkins or GitHub Actions ensure that code changes are automatically tested and integrated, maintaining code quality and stability.”

These top 10 interview questions for C++ developers cover a range of fundamental and advanced topics. By asking these questions and carefully assessing the answers, you can identify candidates with the technical skills and experience necessary for your C++ projects. Additionally, understanding the nuances in their responses will help you gauge their problem-solving abilities and their readiness to tackle complex development challenges.

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• C++ Data Types
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Is assignment operator inherited?

In C++, like other functions, assignment operator function is inherited in derived class.

For example, in the following program, base class assignment operator function can be accessed using the derived class object.

Output: base class assignment operator called

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Inheritence of the move assignment operator in C++

I require some help in understanding the process of inheritance of move assignment operator. For a given base class

I am not quite sure how to invoke base move assignment operator inside the derived class? Should I just use scope operator and say

followed by the subsequent std::move(...) of the additional items defined in Derived class, or is there some other method?

• inheritance
• move-assignment-operator

• 1 Your hand written definition is illustrative? As written {std::move(rhs); return *this;} doesn't move anything –  StoryTeller - Unslander Monica Commented Jun 14, 2018 at 9:54
• Yes, std::move(rhs) is an abbreviation for item_i=std::move(rhs.item_i), where i goes over all data members in Base class. I apologize if I did not make that clear. –  Akhaim Commented Jun 14, 2018 at 10:04
• 2 std::move(rhs) is an abbreviation Please don't use abbreviations like this. Sincerely, the world. –  n. m. could be an AI Commented Jun 14, 2018 at 10:05
• static_cast<Base&>(*this) = std::move(rhs); –  rustyx Commented Jun 14, 2018 at 10:33

To invoke inherited operator= , you normally invoke inherited operator= .

It doesn't matter if it's a copy assignment, a move assignment, or some kind of user-defined assignment, the pattern is the same.

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