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Hello everyone.



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So we have discussed about polymorphism in the last two videos.



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I hope that is clear now.



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And we have also started discussing about virtual functions.



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So what are ritual functions.



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So virtual functions are those functions that are present in the base class and they're overwritten



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in the derived classes.



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Okay.



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In this will do I want to discuss about pure virtual functions.



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Okay I want to discuss about pure virtual functions.



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So what are two or which functions.



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So beyond what dual functions are virtual functions but they do not have definitions.



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Okay so the functions that do not have a definition are called Pure virtual function.



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So what is the syntax for creating a function.



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Well tool so we will write the key word virtual and let's say we are talking about the print function



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of difficult class.



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So by writing the keyword by adding the keyword virtual this print function is now of virtual function.



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Okay.



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Now this is a normal virtual function.



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I want to create a pure virtual function.



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So the syntax for creating a pure virtual function is first of all we will write the keyword virtual



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then let's say I'm converting this function into pure which will function.



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So virtual white print and beyond what your function means they do not have definition.



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So it will not have definition.



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So this is the syntax for creating a pure virtual function okay.



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It will not have definition.



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Now the scene seeing good.



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Okay now let's.



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I'm coming despite so I want to create I want to convert this function and to pure virtual function.



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So we have to remove the definition I am removing the definition and then we do not have a definition.



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Okay.



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So this is pure virtual function no



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okay.



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So this is the syntax for creating a pillar which will function simply no definition at all.



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Okay.



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Now we will see in some time why we need to build a virtual function.



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What is the use case of build virtual function.



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But before we all virtual function let us talk about abstract classes okay.



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What types of classes and why do we need them.



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So let us first try to understand what that abstract classes okay.



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So if a class contain a pure virtual function then that class is an abstract class.



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Okay.



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So if a class contains a pure virtual function then that class will become abstract class.



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So here we call is an abstract class because it is containing a pool which will function.



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Okay simple.



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Now what is the meaning of abstract.



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So abstract means incomplete.



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Okay so this class is an incomplete class.



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Why is incomplete because it is having a function it contains a function that doesn't have definition.



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Okay.



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Now what is the purpose of abstract classes.



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So if a class is an abstract class then if you will try to create the object of the abstract class then



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you will get an error.



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Okay.



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So basically we cannot create object of abstract classes.



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Okay since we call is an abstract class.



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So if we will try to create the object of difficult class you will get an error.



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Okay.



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So if you will write we call v you will get an error and that it will be that we call class is an abstract



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class so you cannot create the object of the F classes.



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Okay.



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Now let's see called



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so let us come into everything



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okay.



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So we have only we call we.



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Okay now let us try to run this file so the output will be that we could class.



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We will get an error and that will be.



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So let's see that it so that it is because class is an abstract class and we cannot create the object



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of the abstract classes.



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Okay.



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Simple enough.



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Now there is one more thing that will happen since so this is we cut glass and we have a glass cut which



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in height from the we clicked glass we could Glass has now become an abstract glass because it contains



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a pure virtual function.



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Okay.



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No glass.



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God has two options glass God has two options.



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First option is that it will implement all the pure white gel function of the wickedness so implement



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all the pure virtual functions of difficult glass all pure virtual functions of because less.



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Okay now the second way the second option is it will not implement all pure white will function.



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So what will happen this glass car will become abstract glass.



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It will also become abstract glass okay.



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So Glass car has two options.



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First first option is implement all the power watch and function of the vehicle glass.



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Then in that case the glass car will become a normal glass and then we can create the object of the



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car glass.



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The second option is if it will not implement all the pillar which will function if it will not give



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the definition of purely virtual function.



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Then in that case it will become an abstract class.



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Okay.



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And we will not be able to create the object of the car class.



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Okay so in this case we can see here brain function is a pure virtual function and the class card is



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giving the definition of B all right dual function all the poor which is function of the vehicle class.



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So in this case this is a normal class.



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This is right.



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But if you will remove the print it will remove the implementation of the print function.



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Then the car C will throw this added value because it dies also become an abstract class incomplete



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class.



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Why it has become an abstract class because if will see the structure of the car.



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Class you can see very carefully that this is class got since this class got inherits from the vehicle



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class and we could class has a function has an incomplete function so the class card also has this incomplete



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function.



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Okay.



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This class card also has this incomplete function.



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The class is an abstract class also so we cannot create the object of the car class.



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Okay.



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Now let's see in code so.



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Okay so let's remove the definition



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since.



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Okay so first we have definition since we have a definition we can create the object of the car class.



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Okay so if we will write Ghazi then this is right.



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Okay so our goal will be working.



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So what code is working.



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Okay.



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Now if I will remove this print function.



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So this car class has also become and have class and this time it will run this file.



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We will get an added.



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Okay so we are getting an edit and let's see that it so the class card is an abstract class.



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Okay.



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Okay.



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So now we have understood what our what dual functions and what that abstract classes.



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Okay so one more thing.



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What are beautiful classes.



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Okay so there is something called pure abstract classes so we know where that abstract class there is



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something called pure abstract classes what are pure abstract classes.



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So since the vehicle we call is a beautiful class because it has only one function and that function



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is a pure function pure ritual function.



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Okay so pure abstract class means if an abstract class has all the functions as below what you'll function



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so all functions will be pure virtual then that class will be pure after class.



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Okay.



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So this vehicle.



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Okay so we have this we could class this vehicle.



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Class can have many functions.



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Okay let's say brain function and let's say getters and setters okay.



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So this brain function is a virtual build virtual function.



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Okay.



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So this this is a pure virtual function.



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Various trendsetter they have definitions so they are not pure virtual function.



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So in that case this class is only abstract class.



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We'll call this class only abstract class via abstract because it is containing a pure virtual function.



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But if the getters and setters they are also pure virtual okay.



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If I really make if I will remove the definition of Gordon setter I make them zero then this wicked



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class is containing all the functions as pure virtual functions.



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Then this abstract class will recall less during class.



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Okay so perfect class means all the function of the class will be pure virtual.



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Okay simple enough.



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Now we have understood the meaning of abstract classes and the pure virtual function.



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Now let's see the use case.



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Let's discuss about the use case.



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So in the last video we discussed we took an example of an employee an organization which want to give



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salary to the people and thus any form level were different.



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So they were for employees H.R. manager engineer and others.



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Okay.



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And what we did was we created an employee at a so this was off tape.



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Employee start this was of type employee style so the first index zero was pointing towards an object



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of H.R. plus then manager and then ingenious and others.



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Okay.



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And then we related over this area and then we did then inside the loop we did something like this.



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E to calculate salary function.



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OK we are calling the calculate salary function but with the help of e we can only access we can only



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access the properties of the Employee class that is the base class.



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We can only access the properties of the Employee class only the base class.



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So that's why we have to create a calculate salary function inside the Employee class and that function



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was virtually okay.



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Why.



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Well just because we have to decided the right time that which function to be called.



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Okay.



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So everything was working fine.



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Okay.



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So we cleared it.



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Because we're still functioning inside the Employee class and that function was well still function.



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Okay.



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So everything was fine but I want to what I want to say here is now this calculate salary function should



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be a pure virtual function not only what it should be pure virtual okay why pure virtual because I cannot



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decide what will be the salary inside the Employee class how can I give the definition of conclude salary



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function.



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Okay I cannot give the definition of calculate salary function.



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Okay so since I cannot give the definition what I will do I will make this function as pure virtual



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function.



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Okay.



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Since this function has become the pure virtual function we cannot create our object of type employee.



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Okay we can create we what we have to do we have to create a new class if we want to add another member.



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Okay let's say any other member new stuff or something.



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Okay so this is the use case of pure virtual function.



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There is one modulus case for example if we want to force a child class to implement the function.



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Okay so what do you want to do.



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I have a child class and I want their child class.



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I have a child class and I want that child class to implement a particular function.



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I want to force the child class to implement a particular function what I will do so inside the inside



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the base class I will make this function as pure what will function.



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Okay so that the child the class will be enforced to implement their definition of disputed virtual



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function otherwise the child's class will become the abstract class okay.



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So you can take one more example of how the pure module function can be used for example I have an animal



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class inside the animal.



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We have like Tiger cow hooves.



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Exactly.



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So this animal class has a function.



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Let's say you'd function.



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Okay.



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And the Tiger go and hose.



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Okay.



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They will have the.



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You'd function.



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So what we can do we can make this you'd function as pure virtual.



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Okay because it cannot give their definition of you'd function inside the animal class.



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So we will make this eat function as pure module function in this way the tiger class it will have it



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on its function it will give the definition of its own function call will give the definition of its



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own function and the horse will give the definition of its own function.



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Okay so this is the use case of build which will function.



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Okay so I hope everything is clear.



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No thank you.