#include <fstream>    // DOES fstream include iostream? NO;
#include <iostream>   // (comment this out, to see this!)
#include <cstdlib>    // (so can use exit function)
using namespace std;

// consider: what is DIFFERENT between this opening
//           comment block, and those for io1.cpp, io2.cpp,
//           io4.cpp?
//           What is the SAME?

// Contract: void -> int
// Purpose: read the number of rats and their weights
//          from file "ratWeights.txt" in the current
//          working directory, sum their weights,
//          and print a message to the file 
//          "allRatsWeight.txt" in the current directory
//          including their total weight.
//
// IMPORTANT ASSUMPTIONS: it assumes that ratWeights.txt
//    already exists in the current directory, and that
//    it contains a number of rats, followed by precisely
//    that many rats' weights (as type double). These
//    values must be separated by some kind of white 
//    space.
//
// Examples: if, when started, the file ratWeights.txt
//           contains:
// 4
// 13.3
// 5
// 27.1
// 15.5
//           ...then io5 should print to file 
//           allRatWeights.txt (in the current directory)
//           the message:
// The total weight is 60.9
//
// by: Sharon M. Tuttle
// last modified: 10-28-03

int main()
{
    // declaration section
    float   weight, total = 0;
    int     num_rats;

    // we declare an ifstream variable, an input 
    //    file stream variable, giving it the name 
    //    input_stream
    ifstream input_stream;

    // we declare an ofstream variable, an output file 
    //    stream variable, giving it the name output_stream
    ofstream output_stream;

    // open the input and output streams using their
    //    respective open functions
    input_stream.open("ratWeights.txt");
    if (input_stream.fail())
    {
        cout << "Could not open ratWeights.txt for input..."
	     << endl;
        exit(1);
    }

    output_stream.open("allRatWeights.txt");
    if (output_stream.fail())
    {
        cout << "Could not open allRatWeights.txt for"
             << " output..." << endl;
        exit(1);
    }

    // if REACH here --- then successfully opened
    //    BOTH input file and output file;

    // how many rats are there? I read it from the 
    //    FILE, using the input file stream, instead of 
    //    from cin
    //
    // note how I do *NOT* use a prompt, here...

    input_stream >> num_rats;

    // get each rat's weight, accumulate sum of weights
    for (int i=0; i < num_rats; i++)
    { 
	// read in each rat's weight from input file 
        //    stream instead of cin --- again, NO prompt 
        //    is necessary;
	input_stream >> weight;
	total += weight;
    }       
    
    // report the sum of all the rats' weights, but to
    //    the output file stream instead of to
    //    cout! (Notice how, once you set it up, you treat
    //    it like cout...)
    output_stream <<  "The total weight is " << total 
                  << endl;

    // then, when you are done with it, you should 
    //    input and output file streams...
    input_stream.close();
    output_stream.close();

    return 0;
}