// append.cpp -- append information to a file
#include <iostream>
using namespace std;
#include <fstream>
#include <cstdlib>      // (or stdlib.h) for exit()

const char * file = "guests.dat";
const int Len = 40;
int main()
{
    char ch;

// show initial contents
    ifstream fin;
    fin.open(file);

    if (fin.is_open())
    {
        cout << "Here are the current contents of the "
             << file << " file:\n";
        while (fin.get(ch))
            cout << ch;
    }
    fin.close();

// add new names
    ofstream fout(file, ios::out | ios::app);
    if (!fout.is_open())
    {
        cerr << "Can't open " << file << " file for output.\n";
        exit(1);
    }

    cout << "Enter guest names (enter a blank line to quit):\n";
    char name[Len];
    cin.get(name, Len);
    while (name[0] != '\0')
    {
        while (cin.get() != '\n')
            continue;   // get rid of \n and long lines
        fout << name << "\n";
        cin.get(name, Len);
    }
    fout.close();

// show revised file
    fin.clear();    // not necessary for some compilers
    fin.open(file);
    if (fin.is_open())
    {
        cout << "Here are the new contents of the "
             << file << " file:\n";
        while (fin.get(ch))
            cout << ch;
    }
    fin.close();
    cout << "Done.\n";

    return 0; 
}