#include "stdstuff.h"

int computeConsumption (int initialReading, int finalReading) {

    if (finalReading < initialReading) {
         // correct the final reading
         finalReading += 10000;
    }
    return finalReading - initialReading;

}


double computeCost (int gasConsumed) {

    if (gasConsumed <= 70) {
        return 5.0;
    }

    if (gasConsumed <= 170) {
        return 5.0 + ((gasConsumed - 70) * 0.05);
    }

    if (gasConsumed <= 400) {
        return 5.0 + (100 * 0.05) + ((gasConsumed - 170) * 0.025);
    }

    // more than 400 cubic metres consumed
    return 5.0 + (100 * 0.05) + (230 * 0.025) + 
                   ((gasConsumed - 400) * 0.015);

}


void processReadings (int initialReading, int finalReading) {

      int gasConsumed;
      double amountDue;

      gasConsumed = computeConsumption (initialReading, finalReading);
      amountDue = computeCost (gasConsumed);
      cout << setiosflags (ios::fixed | ios::showpoint)
              << setprecision(2)
              << endl << "Cubic metres consumed: "
              << gasConsumed
              << "  Amount Due: " << amountDue << endl;
      // no return required because this is a void function

}


int main () {

    int initialReading, finalReading;

    for (;;) {

        cout << endl << "Enter initial and final readings (-1 -1 to stop): ";
        cin >> initialReading >> finalReading;

        if ((initialReading < 0) || (finalReading < 0)) {
            break;
        }

        processReadings (initialReading, finalReading);

    }

    pause();
    return 0;
}