Fatal error: TRandom3.h: No such file or directory #include <TRandom3.h>

[ksmith]

I assume you are trying to link ROOT libraries into your Geant4 project.

What does your CMakeLists.txt look like? Did you appropriately update the search paths for include files?

Have you looked at this example?

Also just as an FYI here is how to post code snippets, including errors:

Getting the same histograms after cuts

Remark on the way to post code snippets: When you post pieces of code on the forum enclose it with ``` . That makes your post much more readable (I systematically edit your posts that way) . So do: ``` // this is a C++ piece of code. ``` And it will display as: // this is a C++ piece of code.