一个简单的解密程序

加密过程：

#include<iostream>
#include<fstream>
void main(void)
{ 
 char strch,ch;
   int i,x;
 ifstream readfile;
 ofstream writefile; 
 readfile.open("1.txt",ios::in | ios::nocreate);  
if(!readfile)  
{ 
cerr<<"cannot open thie file for input"<<endl;        
exit(0);    }  
 writefile.open("2.txt",ios::in | ios::nocreate);
 if(!writefile)
 {  
cerr<<"cannot open the file for output"<<endl;  
exit(0);   } 
while(!readfile.eof()) 
{     
ch=readfile.get();      
x=static_cast<int>(ch);   
x=(x+3)%128;
strch=static_cast<char>(x);  
 writefile.put(strch);        
}
}

相应的解密过程：

#include<iostream>
#include<string>
#include<fstream>
void main(void){
   char strch,ch;
   int i,x; 
   ifstream readfile;
   ofstream writefile; 
 
   readfile.open("2.txt",ios::in | ios::nocreate);
   if(!readfile) 
     { 
    cerr<<"cannot open thie file for input"<<endl;       
     exit(0);  
      }
  
   writefile.open("3.txt",ios::in | ios::nocreate);  
   if(!writefile)
      {
    cerr<<"cannot open the file for output"<<endl;
          exit(0);
         }

      while(!readfile.eof()) 
         {
     ch=readfile.get();  
     x=static_cast<int>(ch);
     x=(x-3)%128;   
      strch=static_cast<char>(x);
     writefile.put(strch);       
        } 
      }

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