例题：把一个超市购物的题做成函数。这个题做成函数没有必要，但可以了解输入参数，输出参数，返回值，函数体，还有结构体，ArryList集合，for循环算结果，以及集合里 .count的使用

    class Program

    {

        struct shangpin                  //定义个结构体

        {

            public string mingcheng;

            public int jiage;

            public int shuliang;

        }

        public double  chaoshi(double zongjia)    //定义函数名

        {

                ArrayList al = new ArrayList();   //定义一个集合

                              while (true)

                {

                    shangpin sp = new shangpin();  

                    Console.Write("请输入商品名称：");

                    sp.mingcheng = Console.ReadLine();  

                   Console.Write("请输入商品价格：");

                    sp.jiage = Convert.ToInt32(Console.ReadLine());

                    Console.Write("请输入商品数量：");

                    sp.shuliang = Convert.ToInt32(Console.ReadLine());

                    al.Add(sp);

                    Console.Write("请问是否要结账（Y,N）：");

                    if (Console.ReadLine().ToUpper() == "Y")

                    {  

                       break;

                    } 

                  }

             for (int i = 0; i <al.Count; i++)

                {

                    zongjia += ((shangpin)al[i]).shuliang * ((shangpin)al[i]).jiage;

                }

                return zongjia;

                   }

       static void Main(string [] args)

        {

                       while (true)

           {  

              Console.WriteLine("小小超市欢迎您！");

               double zongjia1 = 0;

               double  zongjia2=new Program().chaoshi(zongjia1);//定义一个变量zongjia2用来接收变量zongjia1调用chaoshi 这个函数计算出来的结果

               Console.WriteLine("您要付出的总价格为" + zongjia1);              

              Console.ReadLine();

           }         }     } }