{
TH1D* h1 = new TH1D("h1", " ", 100, 0, 3); 
h1->FillRandom("gaus");

TH1D* h2 = new TH1D("h2", " ", 100, 0, 3); 
h2->FillRandom("pol1");

// -- This is it (M. Cristinziani)
TGraph g(h1->GetNbinsX(), h2->GetArray(), h1->GetArray());
//but actually has underflow and overflow bins as well !!
//any nice way to avoid that ?

TCanvas c1; 
c1.Divide(2,2); 

c1.cd(1); 
h1->Draw(); 

c1.cd(2); 
h2->Draw(); 

c1.cd(3); 
g->Draw("A*");

}