//
// Program:  english_to_metric
//
// Purpose:  perform conversions from English-system units of distance
//   to their metric equivalents.
//   
// Input/Output:
// The program repeatedly prompts the user to enter one of the
//     following:
//   "i" for inches-to-centimeters conversion
//   "f" for feet-to-meters conversion
//   "m" for miles-to-kilometers conversion
//   "q" to quit
// If the user enters "i", "f", or "m", the program prompts for the
//   distance, performs the conversion, and prints the result.
// If the user enters "q", the program ends.
// If the user enters any other character, the program prints an error 
//   message (and prompts again).
//

#include <iostream.h>
#include <stdlib.h>		// has EXIT_SUCCESS

// See function definitions for comments.
char getCommand(void);
double getDistanceFromUser(void);
double inches2cm(double i);
double feet2m(double f);
double miles2km(double m);

// Main program.
int main(void)
{
  char cmd;			// next "command" -- 'f', 'c', or 'q'

  do
    {
      cmd = getCommand();
      if (cmd == 'i')
	cout << "That distance is "
	     << inches2cm(getDistanceFromUser()) << " centimeters\n";
      else if (cmd == 'f')
	cout << "That distance is "
	     << feet2m(getDistanceFromUser()) << " meters\n";
      else if (cmd == 'm')
	cout << "That distance is "
	     << miles2km(getDistanceFromUser()) << " kilometers\n";
      else if (cmd != 'q')
	cout << "Invalid response\n";
    } while (cmd != 'q');

  return EXIT_SUCCESS;
}

// Function to get the next command from the user.
// Post:  user has been prompted to enter "f", "c", or "q";
//          returns user's response.  
char getCommand(void)
{
  char response;
  cout << "Please choose what to do next:\n"
       << "    i to convert inches to centimeters\n"
       << "    f to convert feet to meters\n"
       << "    m to convert miles to kilometers\n"
       << "    q to quit\n"
       << "Your choice?  ";
  cin >> response;
  return response;
}

// Function to prompt user for a distance to convert.
// Post:  user has been prompted to enter a distance;
//          returns user's response.
double getDistanceFromUser(void)
{
  double dist;
  cout << "Enter the distance to convert:  ";
  cin >> dist;
  return dist;
}

// Function to convert inches to centimeters.
// Pre:  i is a distance in inches.
// Post:  returns equivalent distance in centimeters. 
double inches2cm(double i)
{
  // 1 in = 2.54 cm
  return i * 2.54;
}

// Function to convert feet to meters.
// Pre:  f is a distance in feet.
// Post:  returns equivalent distance in meters.
double feet2m(double f) 
{
  return inches2cm(f * 12) / 100;
}

// Function to convert miles to kilometers.
// Pre:  m is a distance in miles.
// Post:  returns equivalent distance in kilometers.
double miles2km(double m)
{
  return feet2m(m * 5280) / 1000;
}