I am trying to plot a linear fit through five points that have error bars. But it does not appear. Here is my code:

```
# include <iostream>
# include <fstream>
# include <math.h>
# include <iomanip>
# include <cmath>
# include <stdlib.h>
# include <cstdlib>
//# include <fstream.h>
# include <string.h>
# include <string>
//# include <dos.h> //For Sleep()
# include "TROOT.h"
# include "TFile.h"
# include "TTree.h"
# include "TBrowser.h"
# include "TH1.h"
# include "TH2.h"
# include "TH3.h"
# include "TRandom.h"
int main(){
// controls
char inputFileName[50] = "A1_line.dat";
Int_t NumOfLines = 4;
Int_t nArray = NumOfLines + 1;
bool WantToFit = true;
char FitFunc[20] = "[0]*x + [1]";
int xmin = 0;
int xmax = 5;
// create the coordinate arrays
Double_t x[nArray];
Double_t y[nArray];
// create the error arrays
Double_t dx[5] = {0};
Double_t dy[nArray];
ifstream inFile;
inFile.open(inputFileName,ios::in);
if(inFile.is_open()){
cout<<"Input File was opened successfully"<<endl;
}
//Main loop filling arrays from file//
inFile>>x[0]>>y[0]>>dy[0];
cout<<x[0]<<setw(20)<<y[0]<<setw(20)<<dy[0]<<endl;
for(int i = 1; i < NumOfLines; i++){
inFile>>x[i]>>y[i]>>dy[i];
cout<<x[i]<<setw(20)<<y[i]<<setw(20)<<dy[i]<<endl;
}
inFile.close();
// create the canvas
TCanvas *c1 = new TCanvas("c1","A1",200,10,700,500);
c1->SetGrid();
// create the TGraphErrors and draw it
TGraphErrors *gr = new TGraphErrors(nArray,x,y,dx,dy);
gr->SetTitle("A1;X;Y");
gr->SetMarkerColor(4);
gr->SetMarkerStyle(21);
gr->Draw("AP");
// Define Fit Function
if (WantToFit){
TF1 *f = new TF1("f", FitFunc, xmin, xmax);
f->SetParNames("slope","offset");
f->SetParameters(0.5,1);
gr->Fit(f);
}
c1->Update();
return 0;
}
```