// Chapter 2 , Problem 6  (wrk2c.cc)  USING 'if' to handle errors

/* 
-------------Problem------------
  Program needs to read numerator and denominator of 2 fractions,
  then display the product of both fractions as a percent and a
  fraction.

  A valid fraction can not have a zero or negative denominator.
  Zero denominators are handled in a unfriendly way... rejection.

-------------Analysis-----------

DATA REQUIREMENTS
  Constants
    100 = percent decimal adjustment
  Inputs
    2 Numerators (int)
    2 Denominators (int)
  Outputs
    percent (double) - Product of 2 fractions represented as a persent.
    num_product (int) - Product of 2 numerators
    den_product (int) - Product of 2 denominators

FORMULAE
  Nothing more than multiplication of two fractions and integer division.
	

--------------Design-------------

INITIAL ALGORITHM
  1. Get the first fraction from user
  2. Get the second fraction from user
  3. Calculate the fractional representation of the product of the
     two fractions.
  4. Display the result as a fraction.
  5. Calculate the percentage of the product of the two fractions.
  6. Display the percentage result.

REFINEMENTS
------------Implementation---------

KNOWN PROBLEMS
   Entering a floating point number for any numerator or denominator
   is undefined, and makes the program do strange things.
*/

/*
Some preset literals
*/
const int error = 1;
const int ok = 0;

#include <iostream.h>

int main( void )
  { 
  const double percent_adjust = 100.0;//will force conversion to double...
  int num1, den1 , num2 , den2 , num_product, den_product;
  double percent; 


  /*
  Get the first fraction from the user
  */
  cout << "Please enter the numerator of fraction one: ";
  cin >> num1;

  cout << "Please enter the denominator of fraction one (non-zero): ";
  cin >> den1;
  
  //Verify that the denominator of the first fraction was non-zero
  if (den1 == 0)
  { //Report error and terminate program
	cerr<< "Fractions must have a denominator that is not zero!\n";
	return (error);
  }
  // fix up negative, nonzero denominator
  if (den1 < 0)
  {	num1= -num1;
	den1= -den1;
  }

  cout << "Please enter the numerator of fraction two: ";
  cin >> num2;

  cout << "Please enter the denominator of fraction two (non-zero): ";
  cin >> den2;

  //Verify that the denominator of the second fraction was non-zero
  if (den2 == 0)
  { //Report error and terminate program
	cerr<< "Fractions must have a denominator that is not zero!\n";
	return (error);
  }
  // fix up negative, nonzero denominator
  if (den2 < 0)
  {	num2= -num2;
        den2= -den2;
  }

  //We now have two valid fractions
  num_product = num1 * num2;
  den_product = den1 * den2;

  //Display results
  cout  << "The resulting fraction is: " << num_product << "/" << den_product
	<< endl;
  cout  << "Which is " << (percent_adjust*num_product/den_product) << "%" 
	<< endl;

  return ok;
}