Newb problem? histogram from Ntuple

I am trying to draw a histogram from ntuple, I followed this example: … ic2.C.html

I am confused as to why it is saying that
Error: Symbol “c1” is not defined in current scope gain64.c:34:
*** Interpreter error recovered ***

Here is my code. Million thanks in advance.

[code]#include <stdio.h>
#include “TFile.h”
#include “TTree.h”
#include “TGraphErrors.h”
#include “TCanvas.h”

void gain64 (void)
    const char *data_file = "gain.txt";
    TFile *f =TFile::Open(gain_file, "RECREATE");
    const char *gain_file = "gain.root";
    int i=1;
    float date1;
    TTree *ntuple1 = new TTree("ntuple1", "data from ascii file");
    ntuple1->ReadFile(data_file, "date1/f:c1/f:c2/f:c3/f:c4/f:c5/f:c6/f:c7/f:c8/f:c9/f:c10/f:c11/f:c12/f:c13/f:c14/f:c15/f:c16/f:c17/f:c18/f:c19/f:c20/f:c21/f:c22/f:c23/f:c24/f:c25/f:c26/f:c27/f:c28/f:c29/f:c30/f:c31/f:c32/f:c33/f:c34/f:c35/f:c36/f:c37/f:c38/f:c39/f:c40/f:c41/f:c42/f:c43/f:c44/f:c45/f:c46/f:c47/f:c48/f:c49/f:c50/f:c51/f:c52/f:c53/f:c54/f:c55/f:c56/f:c57/f:c58/f:c59/f:c60/f:c61/f:c62/f:c63/f:c64/f");

delete f;
TCanvas *c = new TCanvas("c1", "A Simple Graph Example", 200, 10, 700, 500);

c->Modified(); c->Update();


  1. You use “gain_file” in the “TFile::Open” call, but you first define it in the next line.
  2. When you “delete f;”, the “ntuple1” is automatically deleted, too (so, you must not try to “Draw” it later).
    BTW. The “float date1;” is completely unrelated to the “date1/f:…”.