/*
 * Find real roots of quadratic equation:
 * Prompt for coefficients.
 * Print roots if they exist, else message.  Also do simple checking
 * that input is okay.
 *
 * This version packages the code to solve and print results in
 * a function and solves some examples/tests before prompting.
 *
 * Compile with -lm for sqrt.
 */
#include <stdio.h>
#include <math.h>

/* 
 * function to compute and print roots of a*x*x + b*x + c = 0.
 */
void compute_and_print(double a, double b, double c);

/* main function */
int main(void) {
	printf("program to solve a*x*x + b*x + c = 0\n");
	printf("examples/tests:\n\n");

	/* examples that try to cover all the different possibilities */
	/* 2*x*x - 8 = 0 (two roots) */
	compute_and_print(2.0, 0.0, -8.0);
	/* (2x+1)*(x+5) = 0 (two roots) */
	compute_and_print(2.0, 11.0, 5.0);
	/* 1*x*x + 2 = 0 (no roots) */
	compute_and_print(1.0, 0.0, 2.0);
	/* 1*x*x = 0 (one root) */
	compute_and_print(1.0, 0.0, 0.0);
	/* 2*x - 5 = 0 (linear, one root) */
	compute_and_print(0.0, 2.0, 5.0);
	/* 5 = 0 (does this have a name?  no roots) */
	compute_and_print(0.0, 0.0, 5.0);
	/* 0 = 0 (does this have a name?  all roots) */
	compute_and_print(0.0, 0.0, 0.0);

	double a, b, c;
	printf("enter coefficients a, b, c (floating-point)\n");
	if (scanf("%lf %lf %lf", &a, &b, &c) != 3) {
		printf("error:  non-numeric input\n");
		return 1;
	}
	compute_and_print(a, b, c);
	return 0;
}

void compute_and_print(double a, double b, double c) {
	printf("for a = %f, b = %f, c = %f:\n", a, b, c);
	/* check for cases where the formula does not work */
	if (a == 0) {
		if (b == 0) {
			if (c == 0) {
				printf("all coefficients zero, so everything is a root\n\n");
			}
			else {
				printf("no roots\n\n");
			}
		}
		else {
			printf("one root %f\n\n", -c/b);
		}
	}
	else {
		/* compute discrim and test for < 0 (no roots) */
		double discrim = b*b - 4*a*c;
		if (discrim < 0) {
			printf("no real roots\n\n");
		}
		else if (discrim == 0) {
			printf("one root %f\n\n", -b / (2*a));
		}
		else {
			printf("two roots %f %f\n\n", 
					(-b + sqrt(discrim)) / (2*a),
					(-b - sqrt(discrim)) / (2*a));
		}
	}
}