LESSON 407 OF 409 · PROJECTS: OBJECT-ORIENTED

Shopping Cart in C++ in C++

Practice

A shop keeps its orders in a cart. Build two classes that work together: a LineItem is one row of the cart (a product, its price and how many were bought), and a Cart holds many rows and adds them up. The cart has line items (composition), it is not one.

LineItem

Public fields string name, double price, int quantity.
LineItem(string name, double price, int quantity) stores the three values using this->.
double subtotal() returns price * quantity.

Cart

It keeps its items in a private vector<LineItem> items.
void add(LineItem item) pushes the item onto the vector.
double total() returns the sum of the subtotals of all items: start double sum = 0, loop with for (auto& item : items), return sum.

Rules:

The total is worked out every time it is asked for, from the items in the cart at that moment. Adding an item later changes the next total.
An empty cart has a total of 0.
An item with price 5 and quantity 3 has a subtotal of 15.
Prices in the driver are whole numbers.

Remember the public: and private: labels and the ; after each class. cout prints the double 75 as 75. The driver lives in Solution::mainFunction().

The driver (already in the starter code, don't change it) creates an empty cart, checks one subtotal, then fills a cart and prints the total twice:

class Solution {
public:
    void mainFunction() {
        Cart empty;
        cout << "Empty: " << empty.total() << endl;
        LineItem apple("Apple", 5, 3);
        cout << "Subtotal: " << apple.subtotal() << endl;
        Cart cart;
        cart.add(apple);
        cart.add(LineItem("Bread", 20, 3));
        cout << "Total: " << cart.total() << endl;
        cart.add(LineItem("Milk", 10, 2));
        cout << "Total: " << cart.total() << endl;
    }
};

Expected output:

Empty: 0
Subtotal: 15
Total: 75
Total: 95

Write class LineItem { public: ... }; first, then class Cart.

for (auto& item : items) sum += item.subtotal();

class LineItem {
public:
    string name;
    double price;
    int quantity;

    LineItem(string name, double price, int quantity) {
        this->name = name;
        this->price = price;
        this->quantity = quantity;
    }

    double subtotal() {
        return price * quantity;
    }
};

class Cart {
private:
    vector<LineItem> items;
public:
    void add(LineItem item) {
        items.push_back(item);
    }

    double total() {
        double sum = 0;
        for (auto& item : items) sum += item.subtotal();
        return sum;
    }
};

class Solution {
public:
    void mainFunction() {
        Cart empty;
        cout << "Empty: " << empty.total() << endl;
        LineItem apple("Apple", 5, 3);
        cout << "Subtotal: " << apple.subtotal() << endl;
        Cart cart;
        cart.add(apple);
        cart.add(LineItem("Bread", 20, 3));
        cout << "Total: " << cart.total() << endl;
        cart.add(LineItem("Milk", 10, 2));
        cout << "Total: " << cart.total() << endl;
    }
};

STEP 1 OF 19

Guided

Ctrl + Enter to check