using System;
using System.Collections.Generic;
 
namespace ConsoleApp1
{
    static class MyLinq
    {
        public static IEnumerable<int> Where(this int[] arr, Func<int, bool> cond)
        {
            int[] result = new int[arr.Length];
            int j = 0;
            for (int i = 0; i < arr.Length; i++)
                if (cond(arr[i]))
                    result[j++] = arr[i];
            Array.Resize(ref result, j);
            return result;
        }
    }
 
    class Program
    {
        static bool myfunc(int x)
        {
            return x < 5;
        }
        static void Main(string[] args)
        {
            int[] arr = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
            var query = arr.Where(myfunc);
            foreach (int x in query) Console.Write(x + "\t");
        }
    }
}
 

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