//C++ include
#include <iostream>
#include <fstream>
#include <vector>

using namespace std;

int linear()
{
	vector<double> x, y, ex, ey;
	double auxx, auxy, auxex, auxey;

	ifstream arquivo("data.txt");
	for(int i = 0; !arquivo.eof(); i++)
	{
		arquivo >> auxx >> auxy >> auxex >> auxey;
		x.push_back(auxx);
		y.push_back(auxy); 
		ex.push_back(auxex); 
		ey.push_back(auxey); 
	}
	
	int n = x.size();
	double *px = &x[0];
	double *py = &y[0];
	double *pex = &ex[0];
	double *pey = &ey[0];

	TCanvas c1("Canvas");
	c1.SetTickx();
	c1.SetTicky();
  	c1.SetGrid();
	gROOT -> SetStyle("Classic");

	TGraphErrors *pontos = new TGraphErrors(n, px, py, pex, pey);
	pontos -> SetMarkerColor(kBlack);
  	pontos -> SetMarkerStyle(21);
  	pontos -> SetMarkerSize(0.5);
  	pontos -> SetTitle("Electric Field and Distance");
  	pontos -> GetXaxis() -> SetTitle("d [m]");
  	pontos -> GetYaxis() -> SetTitle("E [N/C]");
  	pontos -> Draw("APE");

	TF1 *f = new TF1("Linear law","[0]*x + [1]", 0, 100);
	f -> SetNpx(700);
	pontos -> Fit(f, "R"); 

	TPaveText stats(0.5, 0.75, 0.7, 0.83,"blrtNDC");
    stats.SetTextSize(0.035);
    stats.SetBorderSize(0.4);
    stats.SetFillColorAlpha(10,0.2);
	double a = f->GetParameter(0);
    double b = f->GetParError(0);
    double c = f->GetParameter(1);
    double d = f->GetParError(1);
    char arr1[100];
    sprintf(arr1,"V = (%.0f #pm %.0f)d + (%.0f #pm %.0f) ", a, b, c, d);
    TText *input2 = stats.AddText(arr1);
	stats.Draw("Same");

	c1.Print("image5_1.png");

	return 0;
}