desc为降序
ASC为升序，默认就是ASC

Main函数
UpsideDown ud=new UpsideDown("F:\\CSharpCode\\BMMS_Pro\\File.txt","F:\\CSharpCode\\BMMS_Pro\\File1.txt"); //提取和输入的文件路径
            ud.reader();
            ud.convert();
            ud.writer();

实现电话号码颠倒的类
public class UpsideDown
{
    private string[] ss=new string[10];
    private string filename;
    private string filename2;
    private int number;

    public UpsideDown(string filename,string f)
    {
        this.filename=filename;
        filename2=f;
    }

    public void reader()
    {
        try
        {
            if(File.Exists(filename))
            {

                using(StreamReader fout=new StreamReader(filename))
                {
                    //StreamReader fout=new StreamReader(File.Open(filename,FileMode.Open));
                    //StreamReader fout=File.OpenText(filename);
                    int i=0;
                    ss[i]=fout.ReadLine();
                    while((ss[i]!=null&&i<ss.Length)&&ss[i]!="")
                    {
                        //(ss[i]=fout.ReadLine())!=""&&
                        
                        Console.WriteLine("The file'content is "+ss[i]);
                        i++;
                        ss[i]=fout.ReadLine();
                    }
                    number=i;
                }
            }
        }
        catch(IOException e)
        {
            Console.WriteLine(e.Message);
        }
    }
        /*finally
        {
            if(s!=null) fout.Close();
        }*/
    public void convert()
    {
        int i=0;
        string temp;
        for(;i<number/2;i++)
        {
            temp=ss[i];
            ss[i]=ss[number-1-i];
            ss[number-1-i]=temp;
        }
        foreach(string s in ss)
        {
            Console.WriteLine(s);
        }
    }


        public void writer()
        {
            try
            {
                if(File.Exists(filename))
                {

                    using(StreamWriter fin=new StreamWriter(File.Open(filename2,FileMode.OpenOrCreate)))
                    {
                        //StreamWriter fin=new StreamWriter(filename)
                        //StreamReader fout=new StreamReader(File.Open(filename,FileMode.Open));
                        //StreamReader fout=File.OpenText(filename);
                        int i=0;
        
                        while(i<ss.Length&&ss[i]!=null&&ss[i]!="")
                        {
                            fin.WriteLine(ss[i]);
                            //ss[i]=fout.ReadLine();
                            //Console.WriteLine(ss.Length);
                            Console.WriteLine("Successfule inpute  "+ss[i]);
                            i++;
                        }
                    }
                }
            }
            catch(IOException e)
            {
                Console.WriteLine(e.Message);
            }
    }

}