void func()
{   
   auto c1 = new TCanvas("canvas","Example",200,10,600,400);
   auto f = new TF1("f","1-exp(-x/[0])",0,10);  
          
   f->SetParameter(0,1);
   f->SetLineColor(38);
   f->Draw();
  
  TLine *line = new TLine(0, 0.5, 10, 0.5);
  line->SetLineWidth(2);
  line->SetLineColor(kRed);  
  line->Draw("same");  
  gPad->Update();

  Double_t* value = Double_t TF1::GetX(Double_t f=0.5, Double_t xmin = 0, Double_t xmax = 0) const

  cout << Form("%d",value) << endl;;
}