q6.c

#include <math.h>
#include <stdio.h>

#define INF 0x6996

/* solve_quadratic(): solve the quadratic equation */
/* returns the number of valid roots */
/* resulting roots are stored in roots[2] */
int solve_quadratic(double a, double b, double c, double roots[2]) {
    double delta;

    /* special case: a == b == c == 0 => infinite roots */
    if (a == 0 && b == 0 && c == 0) return INF;
    /* special case: a == b == 0; c != 0 => no roots */
    if (a == 0 && b == 0 && c != 0) return 0;

    delta = pow(b, 2) - (4 * a * c);
    printf("delta is %.6lf\n", delta);

    if (delta < 0) return 0;
    
    if (delta == 0) {
        roots[0] = roots[1] = (-b) / (2 * a);
        return 1;
    }

    roots[0] = ((-b) + sqrt(delta)) / (2 * a);
    roots[1] = ((-b) - sqrt(delta)) / (2 * a);
    return 2;
}

void solve_a_zero(double b, double c, double roots[4], int *count) {
    /* since a == 0, we need to solve b^2 + c = 0 */
    *count = solve_quadratic(b, 0, c, roots);
}

void solve(double a, double b, double c, double roots[4], int *count) {
    int i, i2;
    double temp_quad_root[2], temp_xq_root[2];

    for (i = 0; i < solve_quadratic(a, b, c, temp_quad_root); ++i) {
        printf("Quad root %d is %.6lf\n", i, temp_quad_root[i]);

        /* we abuse solve_quadratic() to solve x^2 = quad_root[i] */
        for (i2 = 0; i2 < solve_quadratic(1, 0, -temp_quad_root[i], temp_xq_root); ++i2) {
            printf("Root is %.6lf, pushing\n", temp_xq_root[i2]);
            roots[*count] = temp_xq_root[i2];
            (*count)++;
        }
    }
}

double a, b, c;

double roots[4];
int root_count;

int main() {
    printf("Enter a: ");
    scanf("%lf", &a);
    printf("Enter b: ");
    scanf("%lf", &b);
    printf("Enter c: ");
    scanf("%lf", &c);
    
    if (a == 0) {
        solve_a_zero(b, c, roots, &root_count);
    } else {
        solve(a, b, c, roots, &root_count);
    }
    
    if (root_count == INF) {
        printf("Infinity roots exists\n");
    } else {
        printf("%d root%s found: \n", root_count, ((root_count % 2 == 0) ? ("s") : ("")));
        while (root_count) {
            root_count--;
            printf("%.6lf\n", roots[root_count]);
        }
    } 

    return 0;
}