/*
 * (same as quadratic-as-function program, but revised to use
 * function with pointer parameters)
 *
 * program to solve quadratic equation a*x*x + b*x + c = 0 and print
 * roots if any, or a message if no real roots
 *
 * first prints some tests/examples
 * then prompts for a, b, c and computes/prints roots
 */
#include <stdio.h>
#include <math.h>

/* comments on functions with their definitions below */
void compute_and_print_roots(float a, float b, float c);
int compute_roots(float a, float b, float c, float *r1, float *r2);

/* main program */
int main(void) {
	
	float a, b, c;

	/* do some tests/examples first */
	compute_and_print_roots(1, 0, 5);
	compute_and_print_roots(1, 0, -5);
	compute_and_print_roots(4, 0, -1);
	compute_and_print_roots(0, 4, 1);
	compute_and_print_roots(0, 0, 1);
	compute_and_print_roots(0, 0, 0);

	/* now prompt for input */
	printf("enter a b c\n");
	if (scanf("%f %f %f", &a, &b, &c) != 3) {
		printf("not numbers\n");
		return 1;
	}

	compute_and_print_roots(a, b, c);

	return 0;
}

/*
 * compute roots of a*x*x + b*x + c = 0 if possible
 * returns number of roots found
 */
int compute_roots(float a, float b, float c, float *r1, float *r2) {

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

/* 
 * compute and print roots of a*x*x + b*x + c = 0, or a message saying
 * no real roots
 */
void compute_and_print_roots(float a, float b, float c) {

	float r1, r2;
	int num_roots;

	printf("a, b, c = %f, %f, %f\n", a, b, c);
	num_roots = compute_roots(a, b, c, &r1, &r2);
	if (num_roots == 2)
		printf("two roots:  %f %f\n", r1, r2);
	else if (num_roots == 1)
		printf("one root:  %f\n", r1);
	else if (num_roots == 0)
		printf("no real roots\n");
	else
		printf("internal error! number of roots %d\n", num_roots);

}