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

public class Program
{
    public static void Main()
    {

        var list = new List<int> {0,1,2,3,4,5,6,7,8,9};

        var list2 = new List<int> {0,1,2,3,4,5,6,7,8,9};


        FilterList(list);

        list2 = FilterList2(list2);

        Console.WriteLine(list.Count());
        Console.WriteLine(list2.Count());

    }

    private static void FilterList(List<int> filter)
    {
        filter = filter.Where(x=>x != 0).ToList();
    }

    private static List<int> FilterList2(List<int> filter)
    {
        return filter.Where(x=>x != 0).ToList();
    }

}