Doubt

Program.cs

using System;
using System.Collections.Generic;
using System.Linq;

namespace ConsoleApp1
{
    internal class Program
    {
        private static List<Product> list = new List<Product>();

        private static void Main(string[] args)
        {
            while (true)
            {
                Console.WriteLine("menu:");
                Console.WriteLine("1. add");
                Console.WriteLine("2. addchange units and price by id");
                Console.WriteLine("3. delete");
                Console.WriteLine("4. view");
                Console.WriteLine("5.search products");

                Console.WriteLine("--------------------");

                int choice = Convert.ToInt32(Console.ReadLine());

                switch (choice)
                {
                    case 1:
                        Add();
                        break;

                    case 2:
                        change(choice);
                        break;

                    case 3:
                        delete();
                        break;

                    case 4:
                        view();
                        break;

                    case 5:
                        Product product = search();
                        if (product != null)
                        {
                            Console.WriteLine($"Id for Product: {product.name} is {product.id}");
                        }
                        else
                        {
                            Console.WriteLine("Invalid Product Name");
                        }
                        break;
                }
            }
        }

        public static void Add()
        {
            Console.WriteLine("enter name,id,units,price");
            string name = Console.ReadLine();
            int id = Convert.ToInt32(Console.ReadLine());
            int units = Convert.ToInt32(Console.ReadLine());
            double price = Convert.ToDouble(Console.ReadLine());

            Product p = new Product(id, name, units, price);
            list.Add(p);
        }

        public static void change(int id)
        {
            Console.WriteLine("enter id");
            int id1 = Convert.ToInt32(Console.ReadLine());
            Console.WriteLine("enter new unit and price");
            int u = Convert.ToInt32(Console.ReadLine());
            double price = Convert.ToDouble(Console.ReadLine());

            Product productToUpdate = list.Where(x => x.id == id1).FirstOrDefault();

            productToUpdate.price = price;
            productToUpdate.unitinstock = u;
        }

        public static void delete()
        {
            Console.WriteLine("enter id to be deleted:");
            int id = Convert.ToInt32(Console.ReadLine());

            Product productToDelete = list.Where(x => x.id == id).FirstOrDefault();
            list.Remove(productToDelete);
            Console.WriteLine($"{productToDelete} removed");
        }

        public static void view()
        {
            if (list.Any())
            {
                foreach (Product p in list)
                {
                    Console.WriteLine($"Showing Product Details: {p.name},{p.id},{p.price}, {p.unitinstock}");
                }
            }
            else
            {
                Console.WriteLine("--No data in list--");
            }
        }

        public static Product search()
        {
            Console.WriteLine("enter the name of product to be searched");
            string name = Console.ReadLine();

            Product searchProduct = list.Where(x => x.name == name).FirstOrDefault();

            return searchProduct;
        }
    }

    public class Product
    {
        public int id;
        public string name;
        public int unitinstock;
        public double price;

        public Product(int id, string name, int unit, double price)
        {
            this.id = id;
            this.name = name;
            unitinstock = unit;
            this.price = price;
        }
    }
}