foreach.cs

using System;
using System.Collections;
using System.Collections.Generic;
using System.Threading;

namespace ConsoleApp1
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("Hello World!");
            
            var source = new Source(new int[] {2,4,5});

            foreach (var num in source)
            {
                Console.WriteLine(num);
                Thread.Sleep(1000);
            }
        }
    }

    public class Source : IEnumerable<int>
    {
        private readonly int[] _ints;

        public Source(int[] ints)
        {
            _ints = ints;
        }
        public IEnumerator<int> GetEnumerator()
        {
            var rnd = new  Random();
            while (true)
            {
                yield return _ints[rnd.Next(_ints.Length)];
            }
        }

        IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();
    }
}