interface IFilter<I,O>
    {
        void OnInput(object sender, I args);
    }

    class AbstractFilter<I,O> : IFilter<I,O>
    {
        public delegate void InputEventHandler(I args);
        public delegate void OutputEventHandler(O args);

        public event OutputEventHandler Processed;

        public void OnInput(object sender, I args)
        {
            throw new NotImplementedException();
        }
    }

    class IntToDoubleFilter : AbstractFilter<Int32,Double>
    {
        public event AbstractFilter<int, double>.OutputEventHandler Processed;

        public void OnInput(int args)
        {
            Double dbl = Convert.ToDouble(args);
            Processed(args);
        }
    }

    class DoubleToStringFilter : AbstractFilter<Double,String>
    {
        public event AbstractFilter<double, string>.OutputEventHandler Processed;

        public void OnInput(double args)
        {
            String s = args.ToString();
            Processed(s);
        }
    }

    private void button1_Click(object sender, EventArgs e)
    {
        int i = 100000;

        IntToDoubleFilter f1 = new IntToDoubleFilter();
        DoubleToStringFilter f2 = new DoubleToStringFilter();

        f1.Processed += f2.OnInput;
        f2.Processed += ShowString;

        f1.OnInput(i);
     }

     private void ShowString(String str) {
            MessageBox.Show(str);
     }