Quadratic.cpp

/*
 * File: Quadratic.cpp
 * -------------------
 * This program finds roots of the quadratic equation:
 *
 *               2
 *            a x  +  b x  +  c  =  0
 *
 * If a is 0 or if the equation has no real roots, the
 * program prints an error message and exits.
 */

#include <iostream>
#include <cstdlib>
#include <cmath>
#include "error.h"

/* Function prototypes */

void getCoefficients (double & a, double & b, double & c);
void solveQuadratic (double a, double b, double c,
					 double & x1, double & x2);
void printRoots (double x1, double x2);
//void error (const char* msg);

/* Main program */

int main()
{
	double a, b, c, r1, r2;

	getCoefficients (a, b, c);
	solveQuadratic (a, b, c, r1, r2);
	printRoots (r1, r2);

	return (0);
}

/*
 * Function: getCoefficients
 * Usage: getCoefficients(a, b, c);
 * --------------------------------
 * Reads in the coefficients of a quadratic equation into the
 * reference parameters a, b, and c.
 */

void getCoefficients (double & a, double & b, double & c)
{
	std::cout << "Enter coefficients for the quadratic equation:" << std::endl;
	std::cout << "a: ";
	std::cin >> a;
	std::cout << "b: ";
	std::cin >> b;
	std::cout << "c: ";
	std::cin >> c;
}

/*
 * Function: solveQuadratic
 * Usage: solveQuadratic(a, b, c, x1, x2);
 * ---------------------------------------
 * Solves a quadratic equation for the coefficients a, b, and c. The
 * roots are returned in the reference parameters x1 and x2.
 */

void solveQuadratic (double a, double b, double c,
					 double & x1, double & x2)
{
	if (a == 0) error ("The coefficient a must be nonzero.");
	double disc = b * b - 4 * a * c;
	if (disc < 0) error ("This equation has no real roots.");
	double sqrtDisc = sqrt(disc);
	x1 = (-b + sqrtDisc) / (2 * a);
	x2 = (-b - sqrtDisc) / (2 * a);
}

/*
 * Function: printRoots
 * Usage: printRoots(x1, x2);
 * --------------------------
 * Display x1 and x2, which are the roots of the quadratic equation.
 */

void printRoots (double x1, double x2)
{
	if (x1 == x2)
		std::cout << "There is a double root at " << x1 << std::endl;
	else
		std::cout << "The roots are " << x1 << " and " << x2 << std::endl;
}

/*
 * Function: error
 * Usage: error(msg);
 * ------------------
 * Writes the string msg to the cerr stream and then exits the program
 * with a standard status value indicating that a failure has occurred.
 */

/*
void error (const char *msg)
{
	std::cerr << msg << std::endl;
	exit(EXIT_FAILURE);
}
*/