Lightening Bolts on C++

void line(double x1,double y1,double x2,double y2) {
    Iw2DDrawLine(CIwSVec2((int)x1,(int)y1),CIwSVec2((int)x2,(int)y2));
}

void fracture(double ax,double ay,double bx,double by,int k) {
    double bxax=(bx-ax)/5;
    double byay=(by-ay)/4;
    double cx=ax+bxax;
    double cy=ay+byay;
    double dx=bx-bxax;
    double dy=by-byay;
    double dsv=sqrt(bxax*bxax+byay*byay);
    double ndc=atan2(dy-cy,dx-cx+0.01);
    double ex,ey;
    if (IwRand()%2) {
        ex=cx+cos(-M_PI/3+ndc)*dsv;
        ey=cy+sin(-M_PI/3+ndc)*dsv;
    } else {
        ex=cx+cos(M_PI/3+ndc)*dsv;
        ey=cy+sin(M_PI/3+ndc)*dsv;
    }
    if (k>1) {
        fracture (ax,ay,cx,cy,k-1);
        fracture (cx,cy,ex,ey,k-1);
        fracture (ex,ey,dx,dy,k-1);
        fracture (dx,dy,bx,by,k-1);
    } else {
        line (ax,ay,cx,cy);
        line (cx,cy,ex,ey);
        line (ex,ey,dx,dy);
        line (dx,dy,bx,by);
    }
}