using System;
using System.Collections.Generic;
 
namespace Articulos.Cap04.Secuencias
{
    public sealed class FibonacciPares
    {
        public static void Main()
        {
            foreach (long fibonacci in GeneradorNumeroPares (GeneradorFibonacci(6)))
            {
                Console.WriteLine (fibonacci);
            }
        }
 
         // Retorna elemento por elemento de la serie Fibonacci
        // hasta la cantidad especificada en el argumento:
        private static IEnumerable<long> GeneradorFibonacci(long cantidadSerie)
        {
            // Por cada iteración retorna el valor de la serie actual,
            // realiza los cálculos necesarios para generar el siguiente
            // valor de la serie:
            for (int i = 0, fibAnterior = 1, fibActual = 1; i < cantidadSerie; ++i)
            {
                // Retorna el valor actual de la serie Fibonacci:
                yield return fibAnterior;
 
                int fibNuevo = fibAnterior + fibActual;
 
                fibAnterior = fibActual;
                fibActual = fibNuevo;
            }
        }
 
        // Método que comprueba si los números generados por la serie 
        // Fibonacci son pares:
        private static IEnumerable<long> GeneradorNumeroPares(IEnumerable<long> fibonaccis)
        {
            foreach (long fibonacci in fibonaccis)
            {
                if ((fibonacci % 2) == 0)
                {
                    yield return fibonacci;
                }
            }
        }
    }
}

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