#include <iostream>
#include <fstream>

using namespace std;

class OpenError {};
class ArithmeticError {};
class DivideByZeroError : public ArithmeticError {};
class NegativeRootError : public ArithmeticError {
 public:
	NegativeRootError(double val) : value(val) {}
	double getValue() const {return value;}
 private:
	double value;
};

void find_roots(const double a, const double b, const double c, 
					 double &r1, double &r2) throw (ArithmeticError);

int main() {
	ifstream in;
	string   filename;
	double	a, b, c, root1, root2;

	cout << "Please input the file name containing the coefficients:  ";
	cin  >> filename;

	try {
		in.open(filename.c_str());
		if (!in) {
			throw OpenError();
		}
	}
	catch(OpenError) {
		in.clear();
		cerr << "File " + filename + " not found, please re-enter:  ";
		cin  >> filename;
		in.open(filename.c_str());
		if (!in) {
			cerr << "You're a loser\n";
			exit(0);
		}
	}

	in >> c >> b >> a;
	cout << a << " " << b << " " << c << endl;

	if (!in.good()) {
		cout << "Please enter the missing value:  ";
		cin >> a;
		cout << a << " " << b << " " << c << endl;
	}

	try {
		cout << "Before the first call to find_roots\n";
		find_roots(a, b, c, root1, root2);
		cout << "After the first call to find_roots\n";
	}
	catch (DivideByZeroError) {
		cerr << "Error:  find_roots():  coefficient 'a' is zero\n";
		cout << "Before the second call to find_roots\n";
		find_roots(a+1, b, c, root1, root2);
		cout << "After the second call to find_roots\n";
	}
	catch (NegativeRootError e) {
		cerr << "Error:  find_roots():  discriminent has value " << e.getValue()
			  << endl;
	}
	catch (ArithmeticError) {
		cerr << "Error:  find_roots():  unspecified arithmetic error\n";

	}
	catch (...) {
		cerr << "Error:  unknown exception thrown\n";
	}

	cout << "The roots of " << a << "x^2 + " << b << "x + " << c << " are "
		  << root1 << " and " << root2 << endl;

	return 0;
}

void find_roots(const double a, const double b, const double c, 
					 double &r1, double &r2) throw (ArithmeticError) {

	if (a == 0.0) {
		throw DivideByZeroError();
	}

	double denom   = 2.0 * a;
	double discrim = b * b - 4.0 * a * c;

	if (discrim < 0.0) {
		throw NegativeRootError(discrim);
	}

	throw OpenError();

	cout << "Calculating the roots ... \n";

	r1 = (-b + sqrt(discrim)) / denom;
	r2 = (-b - sqrt(discrim)) / denom;
}