// John Bent's CS 110 Hand-out 2
// Blood Alcohol Content calculator, Improved
//
// a simple c++ program to calculate BAC using Widmark's formula
// program limitations - can only calculate for one proof of
// liquor at a time - (i.e. cannot calculate BAC for a person
// who has drank more than one proof of liquor and no error checking for user input

#include<iostream.h>  //allows use of cout & cin
#include<fstream.h>   //allows input & output of external files
#include<iomanip.h>   //allows use of setprecision

// function prototypes
float get_BAC (char, float, float, int, float);  // FUNCTION DEFINITION
// RETURN TYPE IS FLOAT -- TAKES FIVE PARAMETERS
// this function passes by value

void get_user_input(char&, int&, float&, float&, float&); // FUNCTION DEFINITION
// RETURN TYPE IS VOID --  TAKES FIVE REFERENCE PARAMETERS
// this function passes by reference

//declare global variables
const float MALE_RATE = 0.68, FEMALE_RATE = 0.55;  
	//portion of body weight which holds alcohol
	//usually constants are defined like this
char filename[] = "BAC_data.dat"; // file which holds numerical data


int main ()
{
	//variables to be input and modified
	char gender;
	int weight;
	float oz_drunk, proof, time_span;
	
	// start processing code now
	get_user_input(gender, weight, oz_drunk, proof, time_span); // FUNCTION CALL
	
	// the program can now output the result
	cout << endl << endl << endl; // skip some spaces
	cout << "Your BAC after drinking " << oz_drunk
		 << " ounces of " << proof << " proof liquor over a "
		 << time_span << " hour span is: " << endl << endl << "  : "
		 << setprecision(3) // show BAC to only 3 decimal places
		 << get_BAC (gender, oz_drunk, proof, weight, time_span) // FUNCTION CALL 
		 << " BAC." <<endl <<endl;

	return 0;
}


float get_BAC (char gen, float ounces, float pr,  int w, float time)  // FUNCTION HEADER
{
	ifstream infile (filename, ios::in); //local ifstream variable

	float bac, oz_to_pounds, metabolism, blood_gravity,
	      widmark_rate; // local variables

        infile >> blood_gravity >> metabolism >> oz_to_pounds; // read values from infile
	
	if (gen == 'm' || gen == 'M') widmark_rate = MALE_RATE; 
	else widmark_rate = FEMALE_RATE;

	bac =  (ounces * pr * oz_to_pounds * blood_gravity) / 
		(w * widmark_rate) - (time * metabolism);
	
	if (bac < 0) return 0;
	else return bac;
}






void get_user_input (char& gen, int& w, float& oz_consumed, float& pr, float& time)  
// FUNCTION HEADER
{
	// get info from the user now
        cout << "Are you a <m>an or a <w>oman?" << endl << "  :";
        cin >> gen;
        cout << "\nWhat is your weight in pounds?" << endl << "  :";
        cin >> w;
        cout << "\nHow many ounces of alcohol did you drink?" << endl << "  :";
        cin >> oz_consumed;
        cout << "\nWhat was the proof of the alcohol?" << endl << "  :";
        cin >> pr;
        cout << "\nHow many hours have passed since your first drink?"
                 << endl << "  :";
        cin >> time;
}