how to compare the old product(serialized) to new product,If same product means add the quantity only not repeated that product in output for below program

See more:

C#

//PRODUCT CODE

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


namespace ConsoleApplication4
{
[Serializable]
public class Product
{
private string ProductID;
private string ProductName;
private float Price;
private int Quantity;

public Product()
{
}

public void Read()
{
Console.WriteLine("Enter Product ID : ");
ProductID = Console.ReadLine();
Console.WriteLine("Enter Product Name : ");
ProductName = Console.ReadLine();
Console.WriteLine("Enter Price : ");
Price = float.Parse(Console.ReadLine());
Console.WriteLine("Enter Quantity : ");
Quantity = int.Parse(Console.ReadLine());
}

public void Show()
{
Console.WriteLine("{0}\t\t{1}\t\t{2}\t\t{3}", ProductID, ProductName, Price, Quantity);
}
}
}

//MAIN PROGRAM CODE

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.IO;
using System.Runtime.Serialization.Formatters.Binary;


namespace ConsoleApplication4
{
class Program
{
static void Main(string[] args)
{
List<product> list = new List<product>();
int op;
try
{
Stream stream = File.Open("F:\\Product.obs", FileMode.Open);
BinaryFormatter formatter = new BinaryFormatter();
list = (List<product>)formatter.Deserialize(stream);
}
catch (Exception ex)
{
}
do
{
Console.Clear();
Console.WriteLine("1.New product");
Console.WriteLine("2.List All");
Console.WriteLine("0.Exit");
Console.WriteLine("------------------");
Console.WriteLine("Enter Choice : ");
op = int.Parse(Console.ReadLine());
switch (op)
{
case 1:
Product p = new Product();
p.Read();
list.Add(p);
break;
case 2:
Console.WriteLine("Product Details");
Console.WriteLine("--------------------");
Console.WriteLine("ProductID\t ProductName\t Price\t Quantity");
Console.WriteLine("------------------------------------------");
for (int i = 0; i < list.Count; i++)
{
p = list[i];

p.Show();
}
break;
case 0:
Stream stream = File.Open("F:\\Product.obs", FileMode.Create);
BinaryFormatter formatter = new BinaryFormatter();
formatter.Serialize(stream, list);
break;
}
Console.ReadKey();
}
while (op != 0);
}
}
}