Why won't my code accept output for some values?

[fixotherm]

I have this program that gets the roots of a polynomial. In the function to get the roots, I have a condition that asks if a certain array element is equal to zero. It works for some input like
2
1,4,4
but not on this one:
-2,-1,15
By the way, it also works with other values with a negative sign


Plus I see a negative zero in the output. Does it mean anything?

Here is the code: http://ideone.com/B4uCm1
I'm thinking that the problem is somewhere around here:

int  get_rational_roots_size(int polynomial_degree, double polynomial_coefficients[], double possible_roots[], int num_possible_roots)
{
    int i, j, num_rational_roots = 0;
    double quotient_coefficients[polynomial_degree];
 
    quotient_coefficients[0] = polynomial_coefficients[polynomial_degree];
    for(i = 0; i < num_possible_roots; i++)
    {
        for(j=1;j<=polynomial_degree;j++)
        {
            quotient_coefficients[j] = (quotient_coefficients[j-1]*possible_roots[i])+polynomial_coefficients[polynomial_degree-j];
            if(quotient_coefficients[j] == +0 || quotient_coefficients[j] == -0 && j == 2)
            {
                num_rational_roots++;
            }
        } 
    }
    return num_rational_roots;
}
 
void get_rational_roots(int polynomial_degree, double polynomial_coefficients[], double possible_roots[], int num_possible_roots, double rational_roots[])
{
    int i, j, element = 0;
    double quotient_coefficients[polynomial_degree];
 
    quotient_coefficients[0] = polynomial_coefficients[polynomial_degree];
    for(i = 0; i < num_possible_roots; i++)
    {
        for(j=1;j<=polynomial_degree;j++)
        {
            quotient_coefficients[j] = (quotient_coefficients[j-1]*possible_roots[i])+polynomial_coefficients[polynomial_degree-j];
            printf("Result %d = %lf\t", j, quotient_coefficients[j]);
            if(quotient_coefficients[j] == +0 || quotient_coefficients[j] == -0 && j == 2)
            {
                rational_roots[element] = possible_roots[i];
                printf("\nRoot %lf at i = %d, j = %d\n", rational_roots[element], i, j);
                element++;
            }
        }
        printf("\n");
    }
}
 

Ohh. And this is not a homework. Thanks :D

[weaknessforcats]

I'd like to help but the code at http://ideone.com/B4uCm1 won't compile because it is using non-standard array definitions. That is, it s creating arrays on the stack using a non-const value for the number of elements.

double array[num_elements];
 

instead of:

double* array = (double)malloc(num_elements * sizeof(double));
 

Then there are various casts from double to int that generate warning about truncation and possible loss of data.

It's too much for me to fix.

You should read: http://bytes.com/topic/c/insights/77...rrays-revealed

[donbock]

+0.0 is the same as -0.0 for all but certain special conditions.
I don't know if your program involves any of those special cases. To find out, you need to change "+0" to "+0.0"; & similarly for -0.

+0 and -0 (integers) are always exactly the same.

FYI, 1.0/INFINITY is +0.0 while -1.0/INFINITY is -0.0. (INFINITY comes from math.h)

It is usually a bad idea to compare floating point values for equality (==) or inequality (!=).