/*
 * Program to find real roots of quadratic equation, using a function with 
 * pointer arguments.
 */
#include <stdio.h>
#include <math.h>

/* 
 * returns:
 * how many roots were found, unless special case of a, b, c, all zero,
 * then -1
 */
int compute_roots(double a, double b, double c, double *r1, double *r2);

/*
 * print solution 
 */
void print_solution(int num_roots, double r1, double r2);

/* 
 * calculate roots and print 
 */
void demo(double a, double b, double c);

/*
 * main program 
 */
int main(void) {
	demo(1, -1, -6);
	demo(1, 0, 4);
	demo(0, 5, 2);
	demo(0, 0, 0);
	demo(0, 0, 5);

	printf("enter coefficients a, b, c\n");
	double a, b, c;
	if (scanf("%lf %lf %lf", &a, &b, &c) != 3) {
		printf("invalid input\n");
		return 1; /* bail out of program */
	}

	double r1, r2;
	int nroots = compute_roots(a, b, c, &r1, &r2);
	printf("a = %f, b = %f, c = %f\n", a, b, c);
	print_solution(nroots, r1, r2);
	/* in a real program we might do something else with the roots */
	return 0;
}

int compute_roots(double a, double b, double c, double *r1, double *r2) {
	if (a == 0) {
		if (b == 0) {
			if (c != 0) {
				return 0;
			}
			else {
				return -1;
			}
		}
		else {
			*r1 = -c/b;
			return 1;
		}
	}
	else {
		double d = b*b - 4*a*c;
		if (d < 0) {
			return 0;
		} 
		else {
			*r1 = (-b + sqrt(d)) / (2*a);
			*r2 = (-b - sqrt(d)) / (2*a);
			return 2;
		}
	}
}

void print_solution(int num_roots, double r1, double r2) {
	switch (num_roots) {
		case 2:
			printf("two roots %f %f\n", r1, r2);
			break;
		case 1:
			printf("one root %f\n", r1);
			break;
		case 0:
			printf("no roots\n");
			break;
		case -1:
			printf("everything a root\n");
			break;
		default:
			printf("invalid number of roots (should not happen)\n");
	}
}

void demo(double a, double b, double c) {
	double r1, r2;
	int nroots = compute_roots(a, b, c, &r1, &r2);
	printf("a = %f, b = %f, c = %f\n", a, b, c);
	print_solution(nroots, r1, r2);
}