字符串不可变

        static unsafe void Main(string[] args)
        {
            //StringBuilder 可变
            //string 每次修改都将产生一个新的字符串（不可变）
            //*** 所以，对不修改的字符串使用string，否则使用StringBuilder ***

            string s1 = "test";
            fixed (char *p = s1)
            {
                Console.WriteLine("{0:X}-{1}", (int)p, *p);
                //45824CC-t
            }

            s1 = "test2";
            fixed (char* p = s1)
            {
                Console.WriteLine("{0:X}-{1}", (int)p, *p);
                //4582504 - t
            }

            int n1 = 3;
            Console.WriteLine("{0:X}-{1}", (int)&n1, n1);
            //8FF454 - 3

            n1 = 9;
            Console.WriteLine("{0:X}-{1}", (int)&n1, n1);
            //8FF454 - 9

            

            Console.ReadKey();
        }