Event in C#

eventPriceChanged

using System;

namespace test
{
    class Program
    {
        static void Main(string[] args)
        {
            new TestStock().testStock();           
            Console.ReadKey();
        }        
    }

    class PriceChangedEventArgs : EventArgs
    {
        public readonly decimal LastPrice;
        public readonly decimal NewPrice;

        public PriceChangedEventArgs(decimal lastPrice, decimal newPrice)
        {
            LastPrice = lastPrice;
            NewPrice = newPrice;
        }

        public override string ToString()
        {
            return string.Format("Price is changed: Last {0}, New {1}", this.LastPrice, this.NewPrice);
        }
    }
   
    class Stock
    {
        decimal price;

        public decimal Price
        {
            get
            {
                return price;
            }
            set
            {
                if (price == value) return;
                decimal oldPrice = price;
                price = value;
                OnPriceChanged(new PriceChangedEventArgs(oldPrice, price));
            }
        }
        public event EventHandler<PriceChangedEventArgs> PriceChanged;

        protected virtual void OnPriceChanged(PriceChangedEventArgs e)
        {
            var temp = PriceChanged;
            if (temp != null)
            {
                temp(this, e);
            }
        }
    }
   
    class TestStock
    {
        public void testStock()
        {
            var stock = new Stock();
            stock.PriceChanged += stock_PriceChanged;
            stock.Price = 10;
        }
       
        void stock_PriceChanged(object sender, PriceChangedEventArgs e)
        {
            Console.WriteLine(e);
        }
    }
}