//封装的方法

//读取文件的值，放入集合中

        public static IEnumerable<string> ReadLines(string fileName) {

            using (TextReader reader=File.OpenText(fileName)) {

                string line;

                while ((line=reader.ReadLine())!=null) {

                    yield return line;

                }

            }

 }

//调用

 class Program {

        static void Main(string[] args) {

            foreach (var item in ReadLines("~/map/123.txt")) {

                Console.WriteLine(item);

            }

            Console.ReadKey();

 }

//x^n

 public static IEnumerable<int> Power(int number, int exp) {

            int result = 1;

            for (int i = 0; i < exp; i++) {

                result = result * number;

                yield return result;

            }

        }

//调用，结果 2,4,8,16,32

 class Program {

        static void Main(string[] args) {

             foreach (var item in Power(2, 5)) {

                Console.WriteLine(item);

            }

            Console.ReadKey();

 }