Rtools4.0 and Rstan

When I use Rstan, I have some trouble in solve it. Now I use the Rtools 4.0,but I met some problems:
Warning messages:
1: In system(paste(CXX, ARGS), ignore.stdout = TRUE, ignore.stderr = TRUE) :
‘C:/rtools40/usr/mingw_/bin/g++’ not found

Now can you give me some suggestions about the Rtools4.0 and Rstan,and then how to solve it
Thank you very much.

Hi, that warning is harmless and safe to ignore. Did you have any other issues?

OK ,But I also have some troubles about it. When I do a program, The result of one run is very good.
I ran the program through 100 times, but found that some of the results were quite different from the real parameters. Can you give me some suggestions?