using System;

using System.Collections.Generic;

​

public class Program

{

    public static void Main()

    {

        List<Product> products = new List<Product>

        {

            new Product { Id = 1, Name = "Laptop", Price = 999.99M },

            new Product { Id = 2, Name = "Smartphone", Price = 699.99M },

            new Product { Id = 3, Name = "Tablet", Price = 399.99M }

        };

​

        List<CartItem> cart = new List<CartItem>();

        Console.WriteLine("Available Products:");

​

        foreach (var product in products)

        {

            Console.WriteLine($"ID: {product.Id}, Name: {product.Name}, Price: ${product.Price}");

        }

​

        string input;

        do

        {

            Console.WriteLine("\nEnter Product ID to add to cart (or 'done' to finish, 'remove' to remove an item):");

            input = Console.ReadLine();

​

            if (input.ToLower() == "done")

            {

                break;

            }

​

            if (input.ToLower() == "remove")

            {

                Console.WriteLine("Enter Product ID to remove from cart:");

                string removeInput = Console.ReadLine();

​

                if (int.TryParse(removeInput, out int removeProductId))

                {

                    var itemToRemove = cart.Find(item => item.Product.Id == removeProductId);

                    if (itemToRemove != null)

                    {

                        if (itemToRemove.Quantity > 1)

                        {

                            itemToRemove.Quantity--;

                            Console.WriteLine($"{itemToRemove.Product.Name} quantity decreased by 1.");

                        }

                        else

                        {

                            cart.Remove(itemToRemove);

                            Console.WriteLine($"{itemToRemove.Product.Name} removed from cart.");

                        }

                    }

                    else

                    {

                        Console.WriteLine("Product not found in cart.");

                    }

                }

                else

                {

                    Console.WriteLine("Invalid input. Please enter a valid product ID.");

                }

                continue;

            }

​

            if (int.TryParse(input, out int productId))

            {

                var product = products.Find(p => p.Id == productId);

                if (product != null)

                {

                    AddToCart(cart, product);

                    Console.WriteLine($"{product.Name} added to cart.");

                }

                else

                {

                    Console.WriteLine("Product not found.");

                }

            }

            else

            {

                Console.WriteLine("Invalid input. Please enter a valid product ID.");

            }

​

        } while (true);

​

        Console.WriteLine("\nYour Cart:");

        foreach (var item in cart)

        {

            Console.WriteLine($"{item.Product.Name} - Quantity: {item.Quantity} - Total: ${item.Quantity * item.Product.Price}");

        }

​

        decimal total = CalculateTotal(cart);

        Console.WriteLine($"\nTotal Amount: ${total}");

    }

​

    public static void AddToCart(List<CartItem> cart, Product product)

    {

        var existingItem = cart.Find(item => item.Product.Id == product.Id);

        if (existingItem != null)

        {

            existingItem.Quantity++;

        }

        else

        {

            cart.Add(new CartItem { Product = product, Quantity = 1 });

        }

    }

​

    public static decimal CalculateTotal(List<CartItem> cart)

    {

        decimal total = 0;

        foreach (var item in cart)

        {

            total += item.Product.Price * item.Quantity;

        }

        return total;

    }

}

​

public class Product

{

    public int Id { get; set; }

    public string Name { get; set; }

    public decimal Price { get; set; }

}

​

public class CartItem

{

    public Product Product { get; set; }

    public int Quantity { get; set; }

}

​

​