testFirstOrDefault.cs

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

namespace testFirstOrDefault
{
    class Program
    {
        static void Main(string[] args)
        {
            List<test> testList = new List<test>();

            for (int i = 0; i < 4; i++)
            {
                testList.Add(new test(i, ""));
            }

            int[] ValsToTest = { 1, 1, 2, 2 };

            foreach (int i in ValsToTest)
            {
                var t = testList.FirstOrDefault(x => x.TestVal == i);

                Console.WriteLine("T[{0}].Val = [{1}]!", i, t.Val);

                if ("Set!" != t.Val)
                {
                    t.Val = "Set!";
                }
            }

        }
    }

    internal class test
    {
        public test(int t, string v)
        {
            TestVal = t;
            Val = v;
        }

        public int TestVal { get; set; }
        public string Val { get; set; }
    }
}