What is the use of virtual function?

Question

I don't know why and how I should use it....can someone explain in simple terms? (without using complicated formal book definitions 😒)

Answer 1

If you declare a function as virtual, for example:
class Car {
public :
virtual void drive() {cout<<"Car drives";}} ;

Then derived classes can override (replace) this function with their own version:
class BMW : public Car {
public :
virtual void drive() {cout<<"Bmw drives";}} ;

Repeat this process for other types of car.

The cool thing is you can now go :
Car* cars[] = {new Bmw, new Audi, new Ford,..etc..} ;

And you an treat all the different cars as just a collection of cars, like this:
for(int i=0; i < N; i++)
cars[i]->drive() ;

And will print to cout :
BMW drives
Audi drives
Ford drives
..etc..

Note that the cars pointer call in the for loop to drive() does not call the Car::drive() function (to output "Car drives") , but the same function in the derived class, which outputs its own version.

This is called polymorphism and is enabled by the virtual keyword.