Graph not ploting

[CATWIN94]

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ROOT Version: 6.15/01
Platform: Ubuntu

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I am trying to plot on root using my own C++ code. I do the following (which I got from https://root.cern.ch/doc/master/classTGraph2D.html):

#include <TMath.h>
#include <TGraph2D.h>
#include <TRandom.h>
#include <TStyle.h>
#include <TCanvas.h>
#include <TF2.h>
#include <TH1.h>

int main() {
TCanvas *c = new TCanvas("c","Graph2D example",0,0,600,400);
    Double_t x, y, z, P = 6.;
    Int_t np = 200;
    TGraph2D *dt = new TGraph2D();
    dt->SetTitle("Graph title; X axis title; Y axis title; Z axis title");
    TRandom *r = new TRandom();
    for (Int_t N=0; N<np; N++) {
        x = 2*P*(r->Rndm(N))-P;
        y = 2*P*(r->Rndm(N))-P;
        z = (sin(x)/x)*(sin(y)/y)+0.2;
        dt->SetPoint(N,x,y,z);
    }
    gStyle->SetPalette(1);
    dt->Draw("surf1");

    return 0;
}

The program compiles successfully and runs without problem (Process finished with exit code 0), however, nothing is plotted.

I tried many other examples unsuccessfully.

[bellenot]

Add an instance of TApplication and call TApplication::Run() in order to process events:

#include <TMath.h>
#include <TGraph2D.h>
#include <TRandom.h>
#include <TStyle.h>
#include <TCanvas.h>
#include <TF2.h>
#include <TH1.h>
#include <TApplication.h>

int main(int argc, char **argv) {
    TApplication theApp("theApp", &argc, argv);
    TCanvas *c = new TCanvas("c","Graph2D example",0,0,600,400);
    Double_t x, y, z, P = 6.;
    Int_t np = 200;
    TGraph2D *dt = new TGraph2D();
    dt->SetTitle("Graph title; X axis title; Y axis title; Z axis title");
    TRandom *r = new TRandom();
    for (Int_t N=0; N<np; N++) {
        x = 2*P*(r->Rndm(N))-P;
        y = 2*P*(r->Rndm(N))-P;
        z = (sin(x)/x)*(sin(y)/y)+0.2;
        dt->SetPoint(N,x,y,z);
    }
    gStyle->SetPalette(1);
    dt->Draw("surf1");
    theApp.Run();
    return 0;
}