String 类；Math 类；

  static void Main(string[] args)
        {
            while (true)
            {
               /* string x;
                Console.WriteLine("请随便输入：");
                x= Console.ReadLine();
               x=x.Trim();//前边的空格和后面的空格都去掉

                Console.WriteLine(x);
                 */

               /* string x;
                Console.WriteLine("请随便输入：");
                x = Console.ReadLine();
                int i = x.Length;  //字符串有多少位
                Console.WriteLine(i);//注意这里输出的是数字
                */

                /*
                 string x;
                Console.WriteLine("请随便输入："); 
                x = Console.ReadLine();
                x=x.Replace(" ","");//替换成没有空格
                Console.WriteLine(x);
                 */

               /* string x;
                Console.WriteLine("请随便输入：");
                x = Console.ReadLine();
                x = x.ToLower();   //把大写字母换成小写字母
                Console.WriteLine(x);
                */

               /* string x;
                Console.WriteLine("请随便输入：");
                x = Console.ReadLine();
                x = x.ToUpper();//把小写字母换成大写字母
                Console.WriteLine(x);
               */

               /* string x, b, c, d; string e = "";
               
                Console.WriteLine("请输入您的身份证号：");
                 x=Console.ReadLine();
                //e = x.Replace("约里克","我的身份证号是");
               // Console.WriteLine(e);
                b = x.Substring(6,4);
                Console.WriteLine("您的出生年为"+b+"年");
                c = x.Substring(10,2);
                Console.WriteLine("您的出生月为" + c+"月");
                d = x.Substring(12,2);               
                Console.WriteLine("您的出生日为" + d+"日");
                Console.WriteLine("您的出生年月日为"+b+"年"+c+"月"+d+"日");*/

                /*double a, b;
                Console.WriteLine("请输入一个小数：");
                a = Convert.ToDouble(Console.ReadLine());
                b = Math.Ceiling(a);//满足大于a的最小整数
                Console.WriteLine(b);*/

               /* double a, b;
                Console.WriteLine("请输入一个小数：");
                a = Convert.ToDouble(Console.ReadLine());
                b = Math.Floor(a);//满足小于a的最大整数
                Console.WriteLine(b);
                */

               /*double b,d;
                b =Math.PI;//圆周率
                d = Math.Round(b,3);//保留三位小数，四舍五入
                Console.WriteLine(d);
                */

                /*double b, d,e;
                Console.WriteLine("请随便输入一个数：");
                b = Convert.ToDouble(Console.ReadLine());
                d = Math.Sqrt(b);//平方根
                Console.WriteLine(d);
                e=Math.Round(d);//保留0位小数,四舍五入
                Console.WriteLine(e);
                 */

               /* int s;
                DateTime dt = DateTime.Now;//获取当前系统的时间
                Console.WriteLine(dt);
                s = dt.DayOfYear;//今天是今年的第多少天
                Console.WriteLine(s);
                */
               

               /* int s;
                DateTime dt = new DateTime();//将时间初始化
                Console.WriteLine(dt);
                */

               /* string s = Console.ReadLine();
                DateTime dt = new DateTime();
                dt =Convert.ToDateTime(s);//转换为时间的格式
                Console.WriteLine(dt.DayOfYear);//为本年的第几天
                */
                Console.ReadLine();
            }
        }