Heap block modified past request error in C++

Question

I have and QT application with class Solver that solve some numeric problem (Bairstow method for finding roots of the polynomial by finding its distribution to trinomials) but while for smaller instances (5 parameters, in array tabA) it work fine, but when I tried this for larger instances (7 parameters) application crashed. After I run the debugger I get the following message: Heap block at 02989F58 modified at 02989F80 past request 20 I'm not exactly sure what is about (well I suppose I get stack overflow but I'm not sure where and how) but it points to line delete[] Q; delete[] W; here is how debugger pointed it: And here is code of that class methods (the error occurs in main method int Bairstow(*parameters*), which work on class fields and returns number which indicate is solution was found, is not existing or can't be found in given number of iteration) Here's the main method:

int solver::Bairstow(int stopien,double const *tabA, double *tabP,double *tabR, double eps, int N, double p_,double r_)
{
    int i,q, Iter, indpziel=0;
    i=stopien; 

    while(i>=0 && tabA[i]==0) 
    {
        i--;
    } 

    if (i<2) { return 1; } 

    double *A=new double[stopien +1]
    for (i=0;i<=stopien;i++)
    {
        A[i]=tabA[i];
    }
    double *Q=new double[stopien-1 +1];
    double *w=new double[stopien-3 +1];
    double Reszta[2]; 
    double dqdp[2], dqdr[2]; 
    double p,r, a,b,c,d;
    while (stopien>=2) 
    {
        p=p_, r=r_; 
        Iter=O;
        do
        {
            PodzielWiel(stopien,A,p,r,Q,Reszta);
            if (fabs(Reszta[1])<eps && fabs(Reszta[0])<eps)
            {
                break; 
            }
            
            PodzielWiel(Stopien-2,Q,p,r,W,dqdr); 
            for (i=Stopien-2;i>=0;i--)
            {
                Q[i+1]=Q[i];
            }
            Q[0]=0; 
            PodzielWiel(Stopien-1,Q,p,r,W,dqdp); 
            q=LiczMOdwrotna(dqdp[0],dqdr[0],dqdp[1],dqdr[1],a,b,c,d);
            if (q==1) 
            { 
                delete[] Q; 
                delete[] W;
                return 2;
            }
            p = p-(a*Reszta[0]+b*Reszta[1]); 
            r = r-(c*Reszta[0]+d*Reszta[1]); 
        } while (++Iter<N);
        if (Iter==N) return 3; 

        tabP[IndDziel]=p;
        tabR[IndDziel]=r;
        IndDziel++;
        Stopien-=2;
        for (i=0;i<=Stopien;i++)
        {
            A[i]=Q[i];
        } 
    }
    delete[] Q; delete[] W; //that's the line debugger pointed to
    return 0; 
}

And two helper methods:

1. for polynomial division (by trinomial x^2-px-r)

int solver::PodzielWiel(int stopien,double const *tabA, double p,double r, double *Q,double *R) 
{ 
    if (Stopien<O) return 1; 
    
    int i;
    for (i=0;i<=stopien-2;i++)
    { 
        Q[i]=0;
    }

    while (stopien>=0 && tabA[stopien]==0)
    {
        stopien--; 
    }
    if (stopien<2)
    {
        R[0]=tabA[0];
        R[1]=tabA[1]; 
        return 0;
    }

    double *A=new double[Stopien +1]; 
    for (i=0;i<=stopien;i++)
    {
        A[i]=tabA[i];
    }
    Q[stopien-2]=A[stopien];
    if (stopien>2)
    {
        for(i=stopien; i>1; i--)
        {
            Q[i-2]=A[i];
            A[i-1]+=Q[i-2]*p;
            A[i-2]+=Q[i-2]*r; 
        }
        R[1]=A[1];
        R[0]=A[0] ; 
    }
    else
    { 
        R[1]=A[1]+p*Q[0] ;
         R[0]=A[0]+r*Q[0] ; 
    }
    delete [] A; 
    return 0; 
} 
 

2. for inversing the 2x2 matrix(first 4 parameters are inputs and next 4 outputs as it):

int Solver::LiczMOdwrotna(double x,double y,double w,double z, double &a,double &b,double &c,double &d) 
{ 
    if (x*z==y*w)
    {
        return 1;
    }
    if (x*w!=0)
    { 
        c=1/(y-z*x/w);
        a=-z*c/w; 
        d=1/(z-y*w/x);
        b=-y*d/x;
    }
    else if (y*z!=0) 
    {
        a=1/(x-w*y/z);
        c=-w*a/z;
        b=1/(w-z*x/y);
        d=-x*b/y; 
    }
    else if (x==0 && z==0)
    { 
        c=1/y;
        d=0; 
        a=0;
        b=1/w;
    }
    else if (y==0 && w==0)
    {
        a=1/x;
        b=0; 
        c=0;
        d=1/z;
    }
    return 0; 
}

And sory for maybe poor formatting but I have to use OCR software as copying from QT creator was impossible... even after using show in explorer, save file as txt in new localization (to make it visible outside QT Creator) and then doing it again... I still couldn't copy anything...