Can somebody give me test cases or just tell me what is the problem in my program:
#include <iostream>
#include <cmath>

using namespace std;

struct vector
{
    double x;
    double y;
    double z;
};


double dist(vector a, vector b)
{
    double d = sqrt(pow(b.x - a.x, 2) + pow(b.y - a.y, 2) + pow(b.z - a.z, 2));
    return d;
}

double find_d(vector v_normal, vector point)
{
    double minus_d = v_normal.x*point.x + v_normal.y * point.y + v_normal.z * point.z;
    return -minus_d;
}

int main(int argc, char * argv[])
{
    vector C, N, S, V;
    double R;
    cin >> C.x >> C.y >> C.z;
    cin >> N.x >> N.y >> N.z;
    cin >> R;
    cin >> S.x >> S.y >> S.z;
    cin >> V.x >> V.y >> V.z;
    double t1, t2;
    double D = find_d(N, C);

    t1 = (double)(N.x * V.x + N.y * V.y + N.z * V.z - sqrt(20 * N.z * (D + N.x * S.x + N.y * S.y + N.z * S.z) + pow(N.x*V.x+N.y*V.y + N.z*V.z, 2))) / (double)(10.0*N.z);
    t2 = (double)(N.x * V.x + N.y * V.y + N.z * V.z + sqrt(20 * N.z * (D + N.x * S.x + N.y * S.y + N.z * S.z) + pow(N.x*V.x + N.y*V.y + N.z*V.z, 2))) / (double)(10.0 * N.z);

    vector hit1, hit2;
    hit1.x = S.x + t1*V.x;
    hit1.y = S.y + t1*V.y;
    hit1.z = S.z + t1*V.z - 5*t1*t1;

    hit2.x = S.x + t2*V.x;
    hit2.y = S.y + t2*V.y;
    hit2.z = S.z + t2*V.z - 5 * t2*t2;

    if (t1 >= 0)
    {
        if (dist(hit1, C) <= R)
        {
            cout << "HIT";
            return 0;
        }
    }

    if (t2 >= 0)
    {
        if (dist(hit2, C) <= R)
        {
            cout << "HIT";
            return 0;
        }
    }
    cout << "MISSED";
    return 0;
}