using System;

using System.Linq;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        var list = new List<int>(){1, 5, 6, 9, 0, 1, 4, 8};

        list.RemoveElementBiggerThan(5);

        list.ForEach(i => Console.WriteLine(i));

        Console.WriteLine("Hello World");

    }

}

​

    public static class StringListExtensions

    {

        public static void RemoveElementBiggerThan(this List<int> list, int maxValue)

        {

            if (list is null) throw new ArgumentNullException(nameof(list));

​

            for (int i = list.Count - 1; i >= 0; i--)

            {

                if (list[i] > maxValue)

                {

                    list.RemoveAt(i);

                }

            }

        }

​

        // works also on ImmutableList and ReadOnlyList

        public static bool IsPresentValue(this IEnumerable<string> list, string valueToSearch)

        {

            if (list is null) return true;

​

            foreach (var elem in list)

                if (elem == valueToSearch) return true;

​

            return false;  // default return value

        }

    }