#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?
//           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 screen giving
//          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 io4 should print to the screen the
//           message:
// The total weight is 60.9
//
// by: Sharon M. Tuttle
// last modified: 10-28-03

int main ( )
{
    // local declarations
    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;

    // an input file stream needs to be OPENED in 
    //    order to read from it --- this open function 
    //    expects a single string parameter, representing 
    //    the name of the file from which you want to read 
    //
    // PLEASE note an IMPORTANT assumption here: the 
    //    file has ALREADY been filled with data in 
    //    some way, at this point;

    input_stream.open("ratWeights.txt");
    if (input_stream.fail())
    {
        cout << "Could not open ratWeights.txt for input..."
	     << endl;
        exit(1);
    }

    // if REACH here --- then successfully opened
    // input 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 to the screen
    cout <<  "The total weight is " << total << endl;

    // then, when you are done with it, you should 
    // close your input file stream...
    input_stream.close();

    return 0;
}