电文加密

对一行电文进行加密，每个字母转换为字母表中循环右移的第三个字母，如a->d, b->c, …,y->b,z->c，大写字母也按此规律转换。

Copyright vivi_and_qiao liwei
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApplication2电文加密
{
    class Program
    {
        static void Main(string[] args)
        {
            string s;
            char c='a';
            StringBuilder s1 = new StringBuilder();
            Console.WriteLine("请输入");
            s = Console.ReadLine();
            for (int i = 0; i < s.Length; i++)
            {
                if (s[i] >='a' && s[i] <= 'w')
                    c = (char)((int)s[i] + 3);
                if(s[i]>'w'&&s[i]<='z')
                    c=(char)((int)s[i]-22);
                if (s[i] >= 'A' && s[i] <='W')
                    c = (char)((int)s[i] + 3);
                if (s[i] > 'W' && s[i] <= 'Z')
                    c = (char)((int)s[i] -22);
                s1.Append(c.ToString());
            }
            Console.WriteLine("加密后："+s1.ToString());
            Console.ReadKey();
        }
    }
}