predicate

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace WindowsFormsApplication18
{
    class Student
    {
        public String First { get; set; }
        public String Last { get; set; }
        public Int32 ID { get; set; }
        int[] scores = new int[4];
        public int[] Scores
        {
            get { return scores; }
            set { scores = value; }
        }
        public override string ToString()
        {
            return First + " " + Last + " " + ID + " " + Scores.Average();
        }
    }
    class Students<T>
    {
        public T[] GetList()
        {
            return M;
        }
        private T[] M;
        public Students(IEnumerable<T> students)
        {
            M = (T[])students;
        }
        public IEnumerator<T> GetEnumerator()
        {
            //for (int i = 0; i < M.Length; i++)
            //{
            //  yield return M[i];
            //}
            return (M as IEnumerable<T>).GetEnumerator();
        }
        public Students<T> FindAll(System.Predicate<T> match)
        {
            int leng = 0;
            foreach (T k in M)
            {
                if (match(k)) leng++;
            }
            T[] a = new T[leng];
            leng = 0;
            foreach (T k in M)
            {
                if (match(k)) a[leng++] = k;
            }
            return new Students<T>(a);
        }
    }
    class Program
    {
        static void Main(string[] args)
        {
            Student a = new Student();
            a.First = "Daniil";
            a.Last = "Dranga";
            a.ID = 3;
            a.Scores = new int[4] { 3, 4, 5, 5 };
            Student z = new Student();
            z.First = "Ayuka";
            z.Last = "Erdneev";
            z.ID = 4;
            z.Scores = new int[4] { 3, 4, 5, 5 };
            Student[] b = new Student[2];
            b[0] = a;
            b[1] = z;
            Students<Student> mass = new Students<Student>(b);
            Students<Student> ans = mass.FindAll(x => x.ID > 3);
            Student[] l = ans.GetList();
            foreach(Student p in ans)
            {
                Console.WriteLine(p.ToString());
            }
        }
    }
}