// Programmer: Dylan McDonald
// Class & Section: CS 54, Section <n>
// Date: February 13, 2007
// Purpose: To fire up Da Vinci's time machine (learn functions & references)

#include <iostream>
using namespace std;

/* constants */
const double LITERSPERGILL = 0.1421;
const double KILOSPERSTONE = 6.35;
const double CHAINSPERMETER = 20.1168;
const double KILOMETERSPERMETER = 0.001;
const double SECONDSPERHOUR = 3600.0;
const double MAXTANVELOCITY = 2.5;
const double MAXTIMESPACEVELOCITY = 100.0;

/* Part I function - by value */
/* takes the number of gills, converts it, and returns the number of liters */
double gillsToLiters(double gills)
{
  double liters;
  liters = LITERSPERGILL * gills;
  return liters;
}

/* Part I function - by reference */
/* takes the number of gills, converts it, and updates the conversion value */
void gillsToLitersRef(double &conversionValue)
{
  conversionValue = LITERSPERGILL * conversionValue;
}

/* Part II function - by value */
/* takes the number of stones, converts it, and returns the number of kilos */
double stonesToKilos(double stones)
{
  double kilos;
  kilos = KILOSPERSTONE * stones;
  return kilos;
}

/* Part II function - by reference */
/* takes the number of stones, converts it, and updates the conversion value */
void stonesToKilosRef(double &conversionValue)
{
  conversionValue = KILOSPERSTONE * conversionValue;
}

/* Part III function - tangential velocity */
/* takes the number of chains / s, converts it, and returns km / h */
double chainsToKilometers(double chains)
{
  double kilometers;
  /* convert to m / s */
  kilometers = chains * CHAINSPERMETER;
  /* now we go to m / hr */
  kilometers = kilometers * SECONDSPERHOUR;
  /* and to km / h */
  kilometers = kilometers * KILOMETERSPERMETER;
  return kilometers;
}

/* Part III - time/space velocity */
/* takes chains / s, finds the remaning potential, and returns the velocity */
double timeSpaceVelocity(double tanVelocity)
{
  double timeSpace;
  /* find the remaining potential */
  timeSpace = (MAXTANVELOCITY - tanVelocity) / MAXTANVELOCITY;
  /* now find our time/space velocity */
  timeSpace = timeSpace * MAXTIMESPACEVELOCITY;
  return timeSpace;
}

/* our main function :) */
int main()
{
  double chains, gills, stones;
  double liters, kilograms, kilometers, timeSpace;

  /* Part I - ask for gills */
  cout << "How many gills of wine do we have? ";
  cin >> gills;

  /* Part I - convert gills to liters */
  liters = gillsToLiters(gills);
  gillsToLitersRef(gills);
  cout << "So, we have " << liters << " L." << endl;
  cout << "By reference, we get " << gills << " L." << endl;

  /* Part II - ask for stones */
  cout << "How many stones of cheese do we have? ";
  cin >> stones;

  /* Part II - convert stones to kilograms */
  kilograms = stonesToKilos(stones);
  stonesToKilosRef(stones);
  cout << "So, we have " << kilograms << " kg." << endl;
  cout << "By reference, we get " << stones << " kg." << endl;

  /* Part III - ask for chains / s */
  cout << "What is our velocity (in chains / s)? ";
  cin >> chains;

  /* Part III - calculate using chains / s */
  kilometers = chainsToKilometers(chains);
  timeSpace = timeSpaceVelocity(chains);
  cout << "At " << chains << " chains / s, we are going "
       << kilometers << " km / h." << endl;
  cout << "This implies we are travelling across the time-space "
       << "continuum at a rate of " << timeSpace << " yr / s."
       << endl << endl << "Now all we need is a flux capacitor!"
       << endl;

  return 0;
}