特殊引用类型（string）

 private string FuncWithParameters(int param1, String param2, List<string> param3)
        {
            // 我们在这里改变参数值
            param1 = 100;
            param2 = "hello";
            param3.Add("sfs");
            return "thank you for reading me";
        }
        public void Test()
        {
            int intValue = 200;
            String strParam = "hi";
            List<string> list = new List<string>();
            list.Add("Item1");

            FuncWithParameters(intValue, strParam, list);
            Console.WriteLine("param1: " + intValue);
            Console.WriteLine("param2: " + strParam);
            Console.WriteLine("list count: " + list.Count);

            Console.ReadLine();
        }