LESSON 411 OF 413 · 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 with this..
double Subtotal() returns price * quantity.

Cart

It keeps its items in private List<LineItem> items = new List<LineItem>().
void Add(LineItem item) appends the item to the list.
double Total() returns the sum of the subtotals of all items: start double sum = 0, foreach over the 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.

Method names start with a capital letter in C#. The driver lives in Solution.MainFunction(); Console.WriteLine prints the double 75 as 75.

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 = new Cart();
        Console.WriteLine("Empty: " + empty.Total());
        LineItem apple = new LineItem("Apple", 5, 3);
        Console.WriteLine("Subtotal: " + apple.Subtotal());
        Cart cart = new Cart();
        cart.Add(apple);
        cart.Add(new LineItem("Bread", 20, 3));
        Console.WriteLine("Total: " + cart.Total());
        cart.Add(new LineItem("Milk", 10, 2));
        Console.WriteLine("Total: " + cart.Total());
    }
}

Expected output:

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

Write LineItem (fields, constructor, Subtotal) first, then Cart.

foreach (var item in items) sum += item.Subtotal();

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

    public LineItem(string name, double price, int quantity) {
        this.name = name;
        this.price = price;
        this.quantity = quantity;
    }

    public double Subtotal() {
        return price * quantity;
    }
}

class Cart {
    private List<LineItem> items = new List<LineItem>();

    public void Add(LineItem item) {
        items.Add(item);
    }

    public double Total() {
        double sum = 0;
        foreach (var item in items) sum += item.Subtotal();
        return sum;
    }
}

class Solution {
    public void MainFunction() {
        Cart empty = new Cart();
        Console.WriteLine("Empty: " + empty.Total());
        LineItem apple = new LineItem("Apple", 5, 3);
        Console.WriteLine("Subtotal: " + apple.Subtotal());
        Cart cart = new Cart();
        cart.Add(apple);
        cart.Add(new LineItem("Bread", 20, 3));
        Console.WriteLine("Total: " + cart.Total());
        cart.Add(new LineItem("Milk", 10, 2));
        Console.WriteLine("Total: " + cart.Total());
    }
}

STEP 1 OF 18

Guided

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