// foreach denemesi

using System;

using System.Linq;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        var _data = new List<Demo>();

        _data.Add(new Demo{Id = 1, Name="Test 1"});

        _data.Add(new Demo{Id = 2, Name="Test 2"});

        foreach(var item in _data){

            Console.WriteLine("{0} {1}", item.Id, item.Name);

            item.Name = Guid.NewGuid().ToString();

        }

        foreach(var item in _data){

            Console.WriteLine("{0} {1}", item.Id, item.Name);

        }

    }

    public class Demo{

        public int Id {get;set;}

        public string Name {get;set;}

    }

}