C++ for loop stops before reaching end and restarts - c++

Question

I've been poking my nose into working with arrays in c++ and I've been writing a 1D Euler solver code that I wrote in matlab and converting it to c++ as a practice exercise.
This issue is that this for loop is supposed to run until the counter i reaches N_cells-1 but no matter how high I set the number, it always gets to 57, then restarts from 2 and continues doing this until I click on the output screen. I also ran the code with an N_cells number less than 57 and I get an error code which I've included below.
I'm pretty new to arrays and header files in c++ so I'm sure it's something simple, but I just can't find it. I know it's related to the fqL array but I don't know what.
Error when number <57 is used:
#include "stdafx.h"
#include "Flux.h"
#include <iostream>
#include <chrono>
using namespace std;
void Flux(double * q, double y, double R, int N_cells,double * Flux)
{
double qL[3];
double qR[3];
for (int i = 0; i < N_cells - 1; i++) {
//Initialize left and right sides
//-------------------
qL[0] = q[0, i];
qL[1] = q[1, i];
qL[2] = q[2, i];
qR[0] = q[0, i + 1];
qR[1] = q[1, i + 1];
qR[2] = q[2, i + 1];
//-------------------
//Calculate Left side Parameters
//-------------------
double PL;
//double fqL[3];
double cL2;
double HL;
double uL;
PL = (y - 1)*(qL[2] - 0.5 / qL[0] * (qL[1] * qL[1]));
double fqL[3] = { qL[1],
(3 - y)*0.5*(qL[1] * qL[1]) / qL[0] + (y - 1)*qL[2],
y*qL[1] * qL[2] / qL[0] - (y - 1)*0.5*(qL[1] * qL[1] * qL[1]) / (qL[0] * qL[0]) };
cL2 = y * (y - 1)*(qL[2] / qL[0] - 0.5*(qL[1] / qL[0])*(qL[1] / qL[0]));
HL = 0.5*(qL[1] / qL[0])*(qL[1] / qL[0]) + cL2 / (y - 1);
uL = qL[1] / qL[0];
//Calculate Right side Parameters
//-------------------
double PR;
//double fqR[3];
double cR2;
double HR;
double uR;
PR = (y - 1)*(qR[2] - 0.5 / qR[0] * (qR[1] * qR[1]));
double fqR[3] = { qR[1],
(3 - y)*0.5*(qR[1] * qR[1]) / qR[0] + (y - 1)*qR[2],
y*qR[1] * qR[2] / qR[0] - (y - 1)*0.5*(qR[1] * qR[1] * qR[1]) / (qR[0] * qR[0]) };
cR2 = y * (y - 1)*(qR[2] / qR[0] - 0.5*(qR[1] / qR[0])*(qR[1] / qR[0]));
HR = 0.5*(qR[1] / qR[0])*(qR[1] / qR[0]) + cR2 / (y - 1);
uR = qR[1] / qR[0];
//-------------------
//Calculate Roe's Variables
//-------------------------------- -
double u;
double H;
double c;
double rho;
u = (sqrt(qL[1])*qL[2] / qL[1] + sqrt(qR[1])*qR[2] / qR[1]) / (sqrt(qL[1]) + sqrt(qR[1]));
H = (sqrt(qL[1])*HL + sqrt(qR[1])*HR) / (sqrt(qL[1]) + sqrt(qR[1]));
c = sqrt((y - 1)*(H - 0.5*u *u));
rho = sqrt(qL[1] * qR[1]);
//-------------------------------- -
//-------------------------------- -
double g[3] = { u - c, u, u + c };
double v[3][3] = { {1, u - c, H - u * c},
{1, u, 0.5*u*u},
{1, u + c, H + u * c } };
double a[3] = { 0.5 / (c*c)*((PR - PL) - c * rho*(uR - uL)),
(qR[0] - qL[0]) - 1 * (PR - PL) / (c*c),
0.5 / (c*c)*((PR - PL) + c * rho*(uR - uL)) };
double SUM[3];
SUM[0] = g[0] * a[0] * v[0][0] + g[1] * a[1] * v[1][0] + g[2] * a[2] * v[2][0];
SUM[1] = g[0] * a[0] * v[0][1] + g[1] * a[1] * v[1][1] + g[2] * a[2] * v[2][1];
SUM[2] = g[0] * a[0] * v[0][2] + g[1] * a[1] * v[1][2] + g[2] * a[2] * v[2][2];
double Flux[3];
Flux[0,i] = 0.5*(fqL[0] + fqR[0]) - 0.5*SUM[0];
Flux[1,i] = 0.5*(fqL[1] + fqR[1]) - 0.5*SUM[1];
Flux[2,i] = 0.5*(fqL[2] + fqR[2]) - 0.5*SUM[2];
std::cout << i << endl;
}
}