a.cs

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

namespace NetCoreConsoleAp
{
    class Program
    {
        static void Main(string[] args)
        {
            List<int> list = new List<int>();
            Random rnd = new Random();
            for (int i = 0; i < 100000000; i++)
                list.Add(i);
            long l = 0;
            var sw = new Stopwatch();
            sw.Start();

            foreach (var a in list.Where(i => i < 1000))
            {
                unchecked { l += a; }
            }

            sw.Stop();
            Console.WriteLine("LINQ:" + sw.ElapsedMilliseconds);
            sw.Restart();

            foreach (var a in list)
            {
                if (a >= 1000) continue;
                unchecked { l += a; }
            }

            sw.Stop();

            Console.WriteLine("Foreach:" + sw.ElapsedMilliseconds);
        }
    }
}