Virtual Method

C++ virtual Method also known as Virtual Function is a member function declared inside base class that we can redefine(override) in a derived class. In order to declare virtual method we need to use Virtual keyword before the method. Virtual function will only work when we are applying upcasting concept to it. When the function is made virtual, C++ determines which function is to be invoked at the runtime based on the type of the object pointed by the base class pointer.

Syntax
virtual returnType methodName() {
    //Codes
}

Before entering coding part, we need to know a concept called Method overriding. If a child class has the same method as declared in the parent class, it is known as Method Overriding in c++. In other words, If a subclass provides the specific implementation of the method that has been declared by one of its parent class, it is known as method overriding.

NOTE
If we invoke any method present inside a class using pointer instance we need to use -> symbol between object name and class member name.

CODE

EG 1 . Creating 2 classes with a virtual function in the parent class

#include <iostream>
using namespace std;

class BaseClass {
  public:
    virtual void m1() {
        cout << "Base class method invoked" << endl;
    }
};

class DerivedClass : public BaseClass {
  public:
    void m1() {
        cout << "Derived class method invoked" << endl;
    }
};

int main() {
    //UPCASTING
    BaseClass* obj1 = new DerivedClass();
    obj1->m1();
}

OUTPUT
Derived class method invoked

CODE EXPLANATION
In the above code, we created 2 classes called BaseClass and DerivedClass where BaseClass is the parent class of DerivedClass. BaseClass is having a virtual method called m1(). DerivedClass which is the child class of BaseClass is also having a method called m1(). Inside main method we used upcasting to assign child class object to its parent class reference(obj1). Using this pointer instance obj1, we invoked m1() method. If we compile above program, system will take the child class m1() method and it will override parentClass m1() method. Hence we are getting Derived class method invoked text in the console.


Exercises
1. In the Car class add a new virtual method name it RoofType(). Create child classes with different RoofType() like sunroof, convertible etc.

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