your macro should be:
{
auto am241=new TH1F("am241",
"Count Rate;N_{counts};# occurencies",
4095,
-0.5,
6000);
ifstream inp; double x;
inp.open("Am241.txt");
for (int i=1; i<=4095; i++) {
inp >> x;
am241->SetBinContent(i,x);
}
am241->Draw();
}
And you will get:
