oap_labs/Program.cs

using System.Linq;

List<Item> phones = new List<Item>()
{
    new Item("Iphone SE 2020", 24000),
    new Item("Nokia 3310", 2000),
    new Item("Samsung Galaxy S24", 90000),
    new Item("Samsung Z Fold5", 65000),
    new Item("Iphone 15 Pro Max", 139000),
    new Item("Iphone X", 32000),
    new Item("Xiaomi 12T Pro", 60000)
};

/* 1
var sorted = phones.OrderBy(x => x.title).ThenByDescending(x => x.price);
foreach (var a in sorted)
{
    Console.WriteLine(a.title +" - "+ a.price);
}
*/

/* 2
var averageprice = phones.Select(u =>u.price).Average();
Console.WriteLine(averageprice);
*/

/* 3
var sorted = phones.Where(u => u.title.StartsWith("Samsung"));
foreach (var a in sorted)
{
    Console.WriteLine(a.title);
}

Console.WriteLine();

var sorted2 = phones.Where(u => u.title.StartsWith("Iphone"));
foreach (var a in sorted2)
{
    Console.WriteLine(a.title);
}
*/

/* 4
var phoneslist = phones.OrderBy(x => x.price);
foreach (var x in phoneslist)
{
    Console.WriteLine(x.title +" - "+ x.price);
}
*/


var newlist = phones.Where(u => u.price < 50000).Select(u => u);
Console.WriteLine("Смартфоны дешевле 50000:");
foreach (var a in newlist)
{
    Console.WriteLine(a.title +"-"+ a.price);
}




public class Category
{
    public string title { get; set; }

    public Category(string title)
    {
        this.title = title;
    }
}

public class Item
{
    public string title { get; set; }
    public Category category { get; set; }
    public string description { get; set; }
    public double price { get; set; }

    public Item (string title, double price)
    {
        this.title = title;
        this.price = price;
    }
}

public abstract class Person
{
    public string firstName { get; set; }
    public string lastName { get; set; }
    public int age { get; set; }

    public Person(string firstName, string lastName, int age)
    {
        this.firstName = firstName;
        this.lastName = lastName;
        this.age = age;
    }
}

public class Worker : Person
{
    public double salary { get; set; }
    public string position { get; set; }

    public Worker(string firstName, string lastName, int age, double salary, string position) : base(firstName, lastName, age)
    {
        this.salary = salary;
        this.position = position;
    }
}

public class Client : Person
{
    public string numberPhone { get; set; }
    
    public Client(string firstName, string lastName, int age, string numberPhone) : base(firstName, lastName, age)
    {
        this.numberPhone = numberPhone;
    }
}