// test StringBuilder Operating efficiency
        public static void Fun2()
        {
            #region string
            string str = " I love programming !";
            // provide 1 Group methods and properties that can be used to accurately measure run time.
            Stopwatch stopw = new Stopwatch();
            // Start or continue to measure the elapsed time of an interval.
            stopw.Start();
            for (int i = 0; i < 100000; i++)
            {
                str += "Test";
            }
            // Stop measuring the elapsed time of an interval.
            stopw.Stop();
            Console.WriteLine("string Running time: " + stopw.ElapsedMilliseconds.ToString() + " ms ");
            #endregion
            #region StringBuilder
            StringBuilder sbuild = new StringBuilder(" I love programming! ");
            stopw.Reset();
            stopw.Start();
            for (int i = 0; i < 100000; i++)
            {
                sbuild.Append("Test");
            }
            // Stop measuring the elapsed time of an interval.
            stopw.Stop();
            Console.WriteLine("StringBuilder Running time: " + stopw.ElapsedMilliseconds.ToString() + " ms ");
            #endregion
            #region  In the frame type String
            String str2 = " I love programming !";
            stopw.Reset();
            stopw.Start();
            for (int i = 0; i < 10000; i++)
            {
                str2 += "Test";
            }
            stopw.Stop();
            Console.WriteLine("String Running time: " + stopw.ElapsedMilliseconds.ToString() + " ms ");

            // Usage advice: for a large number of character operations in a program   Like splicing   Something like that   Try to use StringBuilder
            #endregion
        }