Console-算法-某个公司采用公用电话传递数据，数据是四位的整数，在传递过程中是加密的

using System;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            int a, i, t;
            int[] aa = new int[4];
            a = Convert.ToInt32(Console.ReadLine());
            aa[0] = a % 10;
            aa[1] = a % 100 / 10;
            aa[2] = a % 1000 / 100;
            aa[3] = a / 1000;

            for (i = 0; i <= 3; i++)
            {
                aa[i] += 5;
                aa[i] %= 10;
            }
            for (i = 0; i < 3 / 2; i++) /*这个交换写的很微妙*/
            {
                t = aa[i];
                aa[i] = aa[3 - i];
                aa[3 - i] = t;
            }

            for (i = 3; i >= 0; i--)
            {
                Console.Write(aa[i]);
            }

        }
    }
}