using System;

using System.Collections.Generic;

using System.Linq;

​

public class Quantity {

    public int? price {get; set;}

    public int amount {get; set;}

}

​

​

public class Program

{

    public static IEnumerable<Quantity> GetQuantities()

    {

        return new List<Quantity>() {

            new Quantity() {amount=2},

            new Quantity() {price =3, amount=4},

        };

    }

    public static void Main()

    {

        Console.WriteLine("Hello World");

        IEnumerable<Quantity> quantities = GetQuantities();

        quantities = quantities.Where(x => x.price != 200);

        Console.WriteLine("\nPrint Companies");

        foreach (Quantity quantity in quantities)

        {

            Console.WriteLine("price {0}, amount {1}", quantity.price, quantity.amount);

            quantity.price = 199;

        }

        Console.WriteLine($"\nSize of qnuanties: {quantities.Count()}");

        Console.WriteLine("\nTry to Print Companies Again");

        foreach (Quantity quantity in quantities)

        {

            Console.WriteLine("price {0}, amount {1}", quantity.price, quantity.amount);

            quantity.amount = 200;

        }

        Console.WriteLine($"\nSize of qnuanties: {quantities.Count()}");

        Console.WriteLine("\nprinting all");

        foreach (Quantity quantity in quantities)

        {

            Console.WriteLine("price {0}, amount {1}", quantity.price, quantity.amount);

        }

    }

}