How to reset the range and size of Bin?

[couet]

As @alex_HXY said you should create h2with the same number of bin as h1.

Also I see that you create h3 with the name "n_energy_p/n". That’s not a good idea to have “/” in histograms’ names. See:

How to draw an object with special characters in its name?

In general it is not a good idea to have object’s name containing special character like “”, “/”, “#” etc … or even have object name starting with a number because they might be not accessible from the ROOT command line. For instance “/” is the separator for directory level in a file therefore an object having a “/” in its name cannot be access from the command line. Nevertheless it may happen that the some object can be named that way and stored in a ROOT file. The following macro show how to…