Cartesian plane

ROOT
1

i need to draw a cartesian plane. it means that the axis zero has to be in the center of the canvas and coincide for both axes. i didn’t find any way to do it. can you help me?
thanks
luca

2 
{
   c = new TCanvas("c","XY plot",200,10,700,500);
   c->SetFillColor(0);
   c->SetBorderSize(2);
   c->SetFrameLineColor(10);
   c->SetFrameBorderMode(0);

   const Int_t n = 4;
   Double_t x[n] = {-1, -3, -9, 3};
   Double_t y[n] = {-1000,  900,  300, 300};
   gr = new TGraph(n,x,y);
   gr->SetTitle("XY plot");
   gr->SetMinimum(-1080);
   gr->SetMaximum(1080);
   gr->Draw("AC*");

   gr->GetHistogram()->GetYaxis()->SetTickLength(0);
   gr->GetHistogram()->GetXaxis()->SetTickLength(0);
   gr->GetHistogram()->GetYaxis()->SetLabelOffset(999);
   gr->GetHistogram()->GetXaxis()->SetLabelOffset(999);
   gr->GetHistogram()->GetXaxis()->SetAxisColor(0);
   gr->GetHistogram()->GetYaxis()->SetAxisColor(0);

   gPad->Update();
   TGaxis *yaxis = new TGaxis(0, gPad->GetUymin(),
                              0, gPad->GetUymax(),
                              gPad->GetUymin(),gPad->GetUymax(),6,"+LN");
   yaxis->Draw();
   TGaxis *xaxis = new TGaxis(gPad->GetUxmin(), 0,
                              gPad->GetUxmax(), 0,
                              gPad->GetUxmin(),gPad->GetUxmax(),510,"+L");
   xaxis->Draw();
}