Simple C/C++ program

[ct]

It was not long time ago that I wrote a simple C/C++ program that uses XOR encryption/decryption ( the detailed post in this topic was interesting). However, I am not so good at programming, I'm just at intermediate or may be even at beginner level. Nowe, someone quoted form seeing the following code that I don't know nothing about escaping special characters, can any one point out

#include<iostream>
#include<cstdlib>
#include<fstream>
#include<cstdio>
using namespace std;
void encryptdecrypt(string& data,string& key)
{
     int keypos = 0;
 
     for(int i = 0;i<data.length();i++)
     {
           data[i] = data[i] ^ key[keypos];
           keypos++;
           if(keypos >= key.length())
              keypos = 0;
     }
}
int main(int argc,char** argv)
{
    string key = "";
 
    char c;
    string data = "";
    if(argc == 1)
    {
        cout << "Usage: progname filename";
        return 0;        
    }            
    cout << "Enter a password : ";
    while((c = getchar()) != '\n' )
    {
       key += c;          
    }
 
    FILE *fp;
    fp = fopen(argv[1],"rb");
    if(fp == NULL)
    {
        cout << "Sorry, File could not be opened.";
        return 0;        
    }   
 
    while(1)
    {
       c = fgetc(fp);
       if(feof(fp))
          break;
       else
          data+=c;        
 
    }
 
    encryptdecrypt(data,key);
 
    fclose(fp);
 
    FILE *fout;
    fout = fopen(argv[1],"wb");
    if(fout == NULL)
    {
        cout << "Sorry, File could not be opened.";
        return 0;        
    }            
    for(int i = 0;i<data.length();i++)
        fputc(data[i],fout);
 
    fclose(fout);
    getchar();
    return 0;
 
}

#include<iostream>
#include<cstdlib>
#include<fstream>
#include<cstdio>
using namespace std;
void encryptdecrypt(string& data,string& key)
{
     int keypos = 0;
     
     for(int i = 0;i<data.length();i++)
     {
           data[i] = data[i] ^ key[keypos];
           keypos++;
           if(keypos >= key.length())
              keypos = 0;
     }
}
int main(int argc,char** argv)
{
    string key = "";
   
    char c;
    string data = "";
    if(argc == 1)
    {
        cout << "Usage: progname filename";
        return 0;        
    }            
    cout << "Enter a password : ";
    while((c = getchar()) != '\n' )
    {
       key += c;          
    }
   
    FILE *fp;
    fp = fopen(argv[1],"rb");
    if(fp == NULL)
    {
        cout << "Sorry, File could not be opened.";
        return 0;        
    }   
       
    while(1)
    {
       c = fgetc(fp);
       if(feof(fp))
          break;
       else
          data+=c;        
            
    }
    
    encryptdecrypt(data,key);
    
    fclose(fp);
    
    FILE *fout;
    fout = fopen(argv[1],"wb");
    if(fout == NULL)
    {
        cout << "Sorry, File could not be opened.";
        return 0;        
    }            
    for(int i = 0;i<data.length();i++)
        fputc(data[i],fout);
        
    fclose(fout);
    getchar();
    return 0;
    
}

To copy to clipboard, switch view to plain text mode 

Also, how can I improve this small program ...
Thanks.