/*
 * Program to find roots of a quadratic equation.
 * No input for now -- input is hardcoded.
 */
#include <stdio.h>
#include <math.h>

void roots(double a, double b, double c);

int main(void) {

    roots(1.0, 0.0, 1.0);
    roots(1.0, 0.0, 4.0);
    roots(1.0, 0.0, 0.0);
    roots(1.0, 0.0, -1.0);
    roots(1.0, -2.0, 1.0);  // (x-1)(x-1) 
    roots(2.0, -5.0, 2.0);  // (2x-1)*(x-2)
    roots(0.0, 1.0, 1.0);
    roots(0.0, 0.0, 1.0);
    roots(0.0, 0.0, 0.0);
    return 0;
}

/* print root(s) of a*x*x + b*x + c = 0, or message if none */
void roots(double a, double b, double c) {

    double discrim = b*b - 4*a*c;

    printf("a = %f, b = %f, c = %f\n", a, b, c);

    if (a == 0) {
        if (b == 0) {
            if (c == 0) {
                printf("everything is a root\n");
            }
            else {
                printf("no real roots\n");
            }
        }
        else {
            printf("root is %g\n", c/b);
        }
    }
    else if (discrim < 0) {
        printf("no real roots\n");
    }
    else if (discrim == 0) {
        printf("one real root:  %g\n", -b / (2*a));
    }
    else {
        printf("two real roots:  %g, %g\n",
                (-b + sqrt(discrim)) / (2*a),
                (-b - sqrt(discrim)) / (2*a));
    }
}