Vigenere加密解密工具

#include <IOSTREAM.H>    
#include <STDLIB.H>    
#include <STDIO.H>    
#include <CTYPE.H>    
#include <STRING.H>    
   
void Encrypt(FILE*,FILE*,char*);  //加密    
void Decrypt(FILE*,FILE*,char*);  //解密    
   
void main()   
{   
       
    cout << "――――――――++ Vigenere Tool ++――――――――" << endl   
         << "|Function: 采用Vigenere算法对文本文件加密与解密   |" << endl   
         << "|Author: 吴丹                                     |" << endl   
         << "|Run: MicroSoft Visual C++ 6.0                    |" << endl   
         << "|Data: 2003.5.5,Version 1.0 Realeased             |" << endl   
         << "|_________________________________________________|" << endl;   
     
   char FILENAME1[25],FILENAME2[25]; /*文件名称*/   
   FILE *fp, *fp2;                   /*文件指针*/   
   char key[25];                        /*密钥容器*/    
      
   char ch;        /*用户确认*/   
   int user;       /*用户确认*/   
         
   cout << "您确定需要使用 ==Vigenere Tool== [y,n]?" << flush;    
   cin >> ch;   
   if(ch != 'y' && ch != 'Y'){   
       cout << "您已退出==Vigenere Tool==,欢迎再次使用!" << endl;   

       return;   
   }   
      
   cout << endl   
        << "==============Vigenere Tool==============" << endl;   
   cout << "可用操作:1------>文件加密" << endl      
        << "         2------>文件解密" << endl   
        << "         3------>Quit Me!" << endl   
        << "请选择[1,2,3]?" << flush;   
   cin >> user;   
   switch( user )   
   {   
      case 1:/*加密操作*/                
            cout << endl    
                 <<"==============Vigenere Tool==============" << endl;   
            cout << "目前操作:1------>文件加密 " << endl;   
            cout << "请输入需加密的文件名(*.txt): " << flush;   
            gets(FILENAME1);   
               
            cout << endl    
                 <<"==============Vigenere Tool==============" << endl;   
            cout << "目前操作:1------>文件加密 "<< endl;   
            cout << "请输入加密后的文件名(*.txt): " << flush;   
            gets(FILENAME2);   
               
            if((fp = fopen(FILENAME1,"r")) == NULL || (fp2 = fopen(FILENAME2,"w"))==NULL)   
            {    
                printf("Can't open file\n");    
                return ;   
            }