// File Name: Streams.cpp
// Ask the names for the input and output files. 
// Reads three numbers from the input file, sums the numbers, and writes the 
// sum to both the screen and the output file specified by the user. 
#include <fstream>
#include <iostream>
#include <cstdlib>

int main() {
    using namespace std;
    char in_file_name[16], out_file_name[16]; // the filenames can have at most 15 chars
    ifstream in_stream;
    ofstream out_stream;

    cout << "This program will sum three numbers taken from an input\n"
         << "file and write the sum to an output file." << endl;
    cout << "Enter the input file name (maximum of 15 characters):\n";
    cin >> in_file_name;
    cout << "\nEnter the output file name (maximum of 15 characters):\n";
    cin >> out_file_name;
    cout << endl;

    // Condensed input and output file opening and checking. 
    in_stream.open(in_file_name);
    out_stream.open(out_file_name);
    if( in_stream.fail() || out_stream.fail() ) {
        cout << "Input or output file opening failed.\n";
        exit(1);
    }

    double firstn, secondn, thirdn, sum = 0.0;
    cout << "Reading numbers from the file " << in_file_name << endl;
    in_stream >> firstn >> secondn >> thirdn;
    sum = firstn + secondn + thirdn;

    /* The following set of lines will write to the screen */
    cout << "The sum of the first 3 numbers from " << in_file_name 
         << " is " << sum << endl;

    cout << "Placing the sum into the file " << out_file_name << endl;

    /* The following set of lines will write to the output file */
    out_stream << "The sum of the first 3 numbers from " << 
              in_file_name << " is " << sum << endl;

    in_stream.close( );
    out_stream.close( );

    cout << "End of Program." << endl;
    return 0;
}