for (string s = Console.ReadLine(); s != ""; s = Console.ReadLine())
{
    // ......
}

------解决方案--------------------
foreach 适合 对象遍历

for适合变量算法遍历

单纯外部 性能问题？？
for(int i = 0; i <a.count; i++)
.count 需要计算
[i] 需要指向！

------解决方案--------------------
测一下不就知道了
C# code

    class Program
    {
        static void Main(string[] args)
        {            
            Console.WriteLine("Press enter to continue testing!");
            do
            {
                For_Each.TestEfficiency();
                Console.WriteLine("-------------------------------------------");
            } while (Console.ReadKey().Key == ConsoleKey.Enter);
        }

        static void TestEfficiency()
        {
            const int COUNT = 100000000;            
            Stopwatch sw = new Stopwatch();
            //改集合类型 ToList()
            var list = Enumerable.Range(1, COUNT).ToArray(); 
            int temp = 0;
            sw.Start();
            for (int i = 0; i < COUNT; ++i) temp = 0 - list[i];
            sw.Stop();
            Console.WriteLine("for circulate elapsed time:{0}", sw.ElapsedMilliseconds);
            temp = 0;
            sw.Restart();
            foreach (var i in list) temp = 0 - i;
            Console.WriteLine("foreach circulate elapsed time:{0}", sw.ElapsedMilliseconds);
        }