Class Inheritance c++ - c++

Question

i have a base class product and a child class multiBuyProduct
class Product
{
public:
Product(std::string name, Amount price);
}
class MultiBuyProduct :public Product
{
public:
MultiBuyProduct(std::string aName, Amount price, int minDiscountedQuantity, int discountedPercent);
now obviously some of the constructor variables are the same but in my main class i assume if i want the functionality of multiBuyProduct i need to call it? or can i call product and pass values for the multiBuyProduct constructor into a parameter that is expecting a product?
Below shows a method where this is used
void ShoppingCart::add(Product p, int quantity, bool end)
{
}
Above is the method i want to sent the parameters to but i dont know if i need to change the code for this method to accept a MultiBuyProduct or ...??
EDIT: sorry forgot to mention 'Amount' is a class that takes two integers
Amount amount(0,1);

Answer 1

You should change ShoppingCart::add something like below, to achieve polymorphic behavior:
void ShoppingCart::add(Product *p, int quantity, bool end)
{
p->doSomething();
// ...
Product *product = p;
product->doSomething();
// ...
}
Usage:
ShoppingCart shoppingCart;
MultiBuyProduct multiBuyProduct("Paper", Amount(0,1), 1, 1);
shoppingCart.add(&multiBuyProduct, 1, true);

Answer 2

You will probably want to add a virtual method in Product, say, Amount Product::calculatePrice(int quantity), and override it in MultiBuyProduct so that it performs the correct calculation based on minDiscountedQuantity. Then, call this method from add(). Furthermore, you need to pass a reference (Product&) or a pointer (Product*) to add() in order for virtual method invocation to work.

Answer 3

You should change a few things.
You need a type of pointer or reference for polymorphic behaviour.
You need to call the base class constructor.
You need to override your virtual methods.
You should watch out for proper memory management once you rely on pointers.
You should try to be const correct.
Consider this example below:
#include <string>
#include <iostream>
#include <vector>
#include <memory>
#include <sstream>
class Product
{
private:
double Price;
std::string Name;
public:
Product(const std::string& name, double price)
: Price(price),
Name(name)
{
std::cout << "Created " << name << " for $" << price << std::endl;
}
virtual std::string GetName() const
{
return Name;
}
virtual double GetPrice() const
{
return Price;
}
};
class MultiProduct :public Product
{
private:
int Quantity;
public:
MultiProduct(const std::string& name, double price, int quantity)
: Product(name, price),
Quantity(quantity)
{
std::cout << "Created " << quantity << "x " << name << " for $" << price << " each." << std::endl;
}
virtual double GetPrice() const
{
return Product::GetPrice() * Quantity;
}
virtual std::string GetName() const
{
std::stringstream s;
s << Product::GetName();
s << " x";
s << Quantity;
return s.str();
}
};
class ShoppingCart
{
private:
std::vector< std::shared_ptr<Product> > Cart;
public:
void Add( std::shared_ptr<Product> product )
{
Cart.push_back( product );
}
void PrintInvoice() const
{
std::cout << "Printing Invoice:" << std::endl;
for( auto it = Cart.begin() ; it != Cart.end() ; ++it )
{
std::cout << (*it)->GetName() << ": " << (*it)->GetPrice() << std::endl;;
}
}
};
int main()
{
ShoppingCart cart;
cart.Add( std::shared_ptr<Product>( new Product( "cheese", 1.23 ) ) );
cart.Add( std::shared_ptr<Product>( new MultiProduct( "bread", 2.33, 3 ) ) );
cart.Add( std::shared_ptr<Product>( new Product( "butter", 3.21 ) ) );
cart.Add( std::shared_ptr<Product>( new MultiProduct( "milk", 0.55, 5 ) ) );
cart.Add( std::shared_ptr<Product>( new Product( "honey", 5.55 ) ) );
cart.PrintInvoice();
std::cout << "Press any key to continue" << std::endl;
std::cin.get();
return 0;
}