//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();
 }