/************************************************************
* ROOT macro to fill a histogram (reads data from file)
*
* Note: function with the same name as the source code
*       can be executed in ROOT just by '.x upf_cv4_hist.cc'
*       or from terminal by 'root upf_cv4_hist.cc'
*
*       Optionally, source file name can be specified in 
*       the function argument: '.x upf_cv4_hist.cc("NAME")'
*       If it is not specified, 'data.dat' is used.
************************************************************/

// main function:
int upf_cv4_hist(const char* fName = "data.dat")
{
	// settings:
	const int nData = 1200;		// max. number of lines in data.dat
	const int nBins = 500;		// number of histogram bins

	double x[nData];	// declaration of an array (size = nData)
	double xMin;	// min and max to determine histogram limits
	double xMax;

	FILE *fin;				// input file descriptor
	fin = fopen(fName,"r");	// open for reading
	if (fin == NULL)
		return 1;		// if the file could not be open

	int N;				// number of lines read so far
	for (N = 0; N < nData; N++)
	{
		// This fscanf reads one double precision number from one line
		// It returns the number of successfully read numbers, i.e. 1 or 0
		if (fscanf(fin,"%lf",&x[N]) != 1)
			break;
		if (N == 0 || xMin > x[N])	// if undefined or if x_N < xMin
			xMin = x[N];
		if (N == 0 || xMax < x[N])
			xMax = x[N];
	}
	fclose(fin);
	printf("Read %i lines from %s.\n",N,fName);
	printf("xMin = %f\nxMax = %f\n",xMin,xMax);

	// declaration of a 1-dimensional histogram:
	// (https://root.cern.ch/doc/master/classTH1.html)
	char title[256];
	sprintf(title,"Histogram with %i bins",nBins);
	TH1D* hist = new TH1D("hist",title,nBins,xMin,xMax);
	hist->GetXaxis()->SetTitle("#it{x}");
	for (int i = 0; i < N; i++)
		hist->Fill(x[i]);		// fill number x[i] into the histogram

	TCanvas* c = new TCanvas("c","Histogram",800,600);	// define window (not necessary)
	hist->Draw();

	return 0;
}