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Hello everyone.



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So in the last video we started discussing about the volume of freedom.



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So we have discussed about compiled them polymorphism.



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Now let's discuss about the runtime polymorphism.



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So what is the meaning offering them polymorphism.



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So it means that I will take the decision at runtime.



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Okay.



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What operations you want to perform will be decided at different time.



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So in the last two year deal we did something like this



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so in the last review we did something like this.



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We created a vehicle pointer and then the vehicle pointer was pointing towards the derived class object



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so we can write like this also.



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So we can start we do this is new called okay.



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So base class pointer is pointing towards a god class object.



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Okay.



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And when we did something like this when we are calling the print function then what will happen.



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So the car and vehicle both have brain functions.



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So when I am writing with two arrow print.



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So the vehicle print function will be called Why Do We Call brain function.



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Because through we do we can only call the properties through we do we can only access those properties



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that are present in vehicle class.



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Okay.



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So why do we call print function will be called because we are deciding at compile time only that this



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we do is an object of type vehicle essentially does it off type vehicle.



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That's why we will call the vehicle brain function.



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Okay.



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Now what I want is I want to take decision at runtime.



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Okay.



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So I want when I write to Arrow print then instead of vehicle print function car class print function



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should we call Okay white car class.



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Because we do this pointing towards a car class object.



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Okay.



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So we do is pointing towards a car class object.



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That's why I want that.



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When I write we do it or print guard last spring function should be called.



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Okay.



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Now this is runtime polymorphism because I am one too big decision at one time.



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Okay now to achieve that in polymorphism we need to take help of virtual functions.



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Okay.



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So first of all let us try to understand what our virtual functions okay.



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So our goal is very simple.



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What is our goal I want when I write we do arrow print then instead of the kill brain function I want



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to call the print function of the card class.



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Okay.



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And via the print function of calculus.



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Because we do is pointing towards a kind of class object.



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Okay.



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Now to achieve this we need runtime polymorphism and to achieve that in time polymorphism.



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We need two big help of virtual functions.



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So now let us discuss about.



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Now let us discuss what that virtual functions.



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So virtual functions are those functions that are present in the base class.



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And that has been overridden in the derived class.



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Okay.



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So these function will be present in the base class and then we will override laws function indeed derived



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class.



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Okay.



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So how to make a function of virtual function.



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So in order to make a function of virtual function we need to write the keyword virtual.



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Okay.



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So where do we do.



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I want to make this print function as a virtual function.



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So I have to write the keyword virtual okay.



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So now this function is a virtual function why because I have written the keyword virtual and also this



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function has been overwritten in the derived class.



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Okay.



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So what is the meaning what we will achieve by writing the keyword virtual.



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Okay.



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So the virtual keyword with the help of virtual keyword.



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I am telling the compiler to take the decision at runtime.



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Okay I will tell the compiler to dig with the editor in time at which print function to be called.



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Okay.



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So what will happen that in time I will go and check which type of object view two points to.



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Okay so at the time when I when I am writing the statement.



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So when the compiler will reach here what will happen at the right time.



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Compiler will go and check what type of what type of object view points to.



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So we two points to discard class object since we are two points to car class object then called Class



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print function will be called.



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Okay.



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Now why I am taking this with at one time because I have written the keyword module and also this function



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has been overwritten in the car class.



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Okay.



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And they're derived class.



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Now when I will run this file what will happen this car class brain function will be called so let's



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send the file so we can see here the output is God.



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Okay.



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So I am repeating myself again.



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So what will happen at that time.



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I will go and check what this voodoo object points to.



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If it is pointing to a car class then countless print function will be called.



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If it is pointing to a vehicle class then we call class brain function will be called.



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Okay now let's see one more example.



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Now what will happen if I if I will remove the print function of the car class.



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Okay.



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So what will happen what will the output of this line we do it opened.



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Okay so let's say in our file so the output is coming out to be we call.



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Okay.



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Okay so the output is coming out to be we call.



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Now let us try to understand.



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So when I write we do error print now which print function will be called.



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So we do is of type we call.



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But since I have written virtually in the base class so I have to take the decision at runtime.



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So we will check at the wrong time.



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So this is God.



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This is we call this is print function and this is the print function of the card.



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So we do is pointing towards a card class object.



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So this time this print function will be called.



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Okay.



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Now then I will remove the print function from the Card class.



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Then what will happen again.



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I will check whether the Card class has a print function.



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No it doesn't have.



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So I will go to its parent class its parent class has print function.



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So this time this print function of the weekly class will be called.



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Okay.



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And output will be weakened if the vehicle last doesn't have brain function then this line will throw



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us at it.



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Okay.



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Now what will happen if I comment the print function of the vehicle.



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Okay.



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Now let's.



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So we have print function inside the car class but we do not have print function for the vehicle class.



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Okay.



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So if I will run this file what will be our output.



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I think we will go down at it.



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Okay.



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Now let us try to understand why so we are getting an edit.



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And if you will see that it so class recall no name to print.



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Okay so what it is saying here is we do not have print function inside that we call class.



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OK.



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We do not have print function inside that we call it lies and we all know we can only access those properties



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that are present in difficult class through V2.



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Okay.



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I am repeating myself.



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We can only access those properties through we do that are present in difficult class and vacant class



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doesn't have any print function.



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Okay.



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So in this way with the help of virtual function we can achieve runtime polymorphism.



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Okay now let us try to.



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Now let's discuss about the use case of virtual function why we will need virtual function and why we



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need runtime polymorphism.



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Okay



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so suppose we have all organization in organization we have different type of employees and what we



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want is we want to convert the salaries of employees at the end of the month and the formula for calculating



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the salaries for different employee is different.



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Okay so suppose we have four type of employees we have a chart we have manager



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we have engineers



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and others.



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Okay.



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So we have four types of employees and we want to calculate the salary for all the four employees and



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the salary formula is different for different employee.



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Okay.



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So how we can solve this problem.



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So what we will do let's say I will make a class EMPLOYEE Okay.



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All the same features all the common features of the four employees.



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It will be present in the Employee class.



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Then we will create four classes H.R. manager engineer and that's okay.



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So we will use inheritance here.



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Okay.



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So H.R. manager engineers have said that they will inherit from the Employee class.



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Okay.



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So we are using inheritance here and all the common features of the employees are present in the Employee



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class.



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Okay.



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Now I have a calculate salary function.



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Okay.



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So I have a function calculate salary.



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Okay.



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So each class will have this function each other will have conferred salary function.



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Manager will also have converged salary function ingenious and others.



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Okay so all the four classes will have this function.



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Okay so called wrote Sally function is a convertible function is a common function.



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Okay now let's say I have one manager in the company in the organization.



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Let's say we have we have one nature and we have three managers let's say we have 20 engineers and that



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staffers.



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Let's say 4.



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So in total we have condemned employees okay.



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Now what we will do we will create an array of pointers.



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Okay.



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So what I will write so we will write I want to create array of pointers so employ that was start let's



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say.



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Name is E..



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This is new employee



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start and guaranteed I'll give I don't date because we have to get employees.



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Okay so this is area of point those.



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Okay.



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So we have Eddie.



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I'll say he's 28 so this is 0 1 2 3 and so on



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so we know that the base class pointer can point to a child class object.



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Okay.



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So this is an area of pointer and a base class pointer can point to a child class object.



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So the index is 0.



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It will point to a charter class object.



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Okay index 1 it will point to a manager class object simply manager and manager.



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And then we will have in juniors and finally at those.



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Okay so why it is so because because we know that the base class point that can point towards a child



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class object.



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Okay.



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So the index 0 is pointing towards a tag class object and next one is pointing towards manager class



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object and so on.



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Okay.



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Now I want to calculate this entity so vote calculating this I leave what do we do we will run a loop



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or this area okay we will run a loop or disarray and inside the loop what I will write I will write



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something like this E I l calculate salary I will call this function yay annual calculate salary.



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So we will write inside the loop e and can get salary.



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Okay now suppose this employee class it also has a good salary function.



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So this employee class also has a calculate salary function and that function is a virtual function.



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Okay that converts a little function inside the Employee class is a virtual function.



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So when I will write the statement the I had a good salary.



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What will happen.



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We will take the decision at runtime that which function will be called.



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Okay.



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Since we have written what Juliette and all the four classes and all the four classes have called cell



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will function.



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So at this line what will happen.



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We will take the decision at runtime that which calculate salary function we have to call.



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Okay so at that time what will happen.



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Which function to be called.



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It will depend upon the type of the object.



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Okay so for index 0 for index 0.



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What will happen.



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So index 0 is pointing towards a chart class object.



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Okay so for index 0 it Jared calculates every function will be called for index 1 manager calculate



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salary function will be called and so on.



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Okay so which function will be called.



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We will decide that on time.



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So it depends upon the type of the object which is present at the item takes.



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Okay so the item makes it really decide which print function will be called okay.



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So I hope the use case of what actual function and random polymorphism is now clear.



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Okay.



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Thank you.