static void Main()
        {
            BaseOperator addop = GenOpFactory.GenOp("+");

            addop.NumberA = 1;
            addop.NumberB = 2;
            Console.WriteLine(addop.OperateInt());

            BaseOperator subOp = GenOpFactory.GenOp("-");

            subOp.NumberA = 2;
            subOp.NumberB = 1;
            Console.WriteLine(subOp.OperateInt());
        }
        public static BaseOperator GenOp(string tag)
        {
            BaseOperator op = null;

            switch (tag)
            {
            case "+":
                op = new AddOp();
                break;

            case "-":
                op = new SubOp();
                break;
            }

            return(op);
        }