C++ Caesar Cipher File encryption and decryption program source code

C++ program for encrypting and decrypting any file using Caesar cipher and any key entered by the user.

You may even use this as an assignment or mini project in B. Tech. or network security subject by adding little gui and improving the source code.  Feel free to use, modify and share the code... Knowledge is always free !!!

 #include<iostream.h>  
 #include<conio.h>  
 #include<fstream.h>  
 class Caesar  
 {  
     public: void encrypt(char *inp,char *out,int key);  
             void decrypt(char *inp,char *out,int key);  
             void readText(char *inp);  
 };  
 void Caesar::encrypt(char *inp,char *out,int key)  
 {  
     ifstream input;  
     ofstream output;  
     char buf;  
     input.open(inp);  
     output.open(out);  
     buf=input.get();  
     while(!input.eof())  
     {  
         if(buf>='a'&&buf<='z')  
         {  
             buf-='a';  
             buf+=key;  
             buf%=26;  
             buf+='A';  
         }  
         output.put(buf);  
         buf=input.get();  
     }  
     input.close();  
     output.close();  
     readText(inp);  
     readText(out);  
 }  
 void Caesar::decrypt(char *inp,char *out,int key)  
 {  
     ifstream input;  
     ofstream output;  
     char buf;  
     input.open(inp);  
     output.open(out);  
     buf=input.get();  
     while(!input.eof())  
     {  
         if(buf>='A'&&buf<='Z')  
         {  
             buf-='A';  
             buf+=26-key;  
             buf%=26;  
             buf+='a';  
         }  
         output.put(buf);  
         buf=input.get();  
     }  
     input.close();  
     output.close();  
     readText(inp);  
     readText(out);  
 }  
 void Caesar::readText(char *inp)  
 {  
     ifstream input;  
     char buf;  
     input.open(inp);  
     cout<<"\n\n <--- "<<inp<<" --->\n";  
     buf=input.get();  
     while(!input.eof())  
     {  
         cout<<buf;  
         buf=input.get();  
     }  
     input.close();  
 }  
 void main()  
 {  
     Caesar a;  
     int choice,key;  
     char inp[30],out[30];  
     clrscr();  
         cout<<"\n Enter input file: ";  
         cin>>inp;  
         cout<<"\n Enter output file: ";  
         cin>>out;  
         cout<<"\n Enter key: ";  
         cin>>key;  
     cout<<"\n\n 1. Encrypt\n 2. Decrypt\n\n Select choice(1 or 2): ";  
     cin>>choice;  
     if(choice==1)  
         a.encrypt(inp,out,key);  
     else if(choice==2)  
         a.decrypt(inp,out,key);  
     else  cout<<"\n\n Unknown choice";  
     getch();  
 }