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

namespace DictionaryPassing
{
    public interface CNum<T>
    {
        T Add(T a, T b);
        T FromInt(int a);
    }

    public interface CReal<T> : CNum<T>
    {
        T Div(T a, T b);
    }

    public struct ComplexReal : CReal<Complex>
    {
        public Complex Div(Complex a, Complex b) { return a/b; }
        public Complex Add(Complex a, Complex b) { return a+b; }
        public Complex FromInt(int a) { return new Complex(a,0); }
    }

    static class Utils
    {
        public static T Avg<T, C>(this IEnumerable<T> xs) where C : CReal<T>, new()
        {
            var real = new C();
            var sum = real.FromInt(0);
            var i = 0;
            foreach (var x in xs) 
            {
                sum = real.Add(sum, x);
                i++;
            }
            return real.Div(sum, real.FromInt(i));
        }
    }

    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine(Enumerable.Repeat(new Complex(1, 1), 100).Take(10).Avg<Complex,ComplexReal>());
        }
    }
}

K>

var items = new [] { new Complex(12, 6), дописать сколько надо, по желанию}; 

Console.Write(items.Take(10).Aggregate(new Complex(0,0), (acc,item) => acc + item));

template<T>
class MyContainer {
  vector<T> items_;

public:
  typedef function<bool(T&)> ForEachDelegate;  // returns true to continue enumeration

  void foreach(ForEachDelegate d) {
    for(auto i = items_.begin(); i != items_.end(); ++i)
      if(!d(*i))
        break;
  }
};