The c file should be quite simple, just trying to produce 2 histograms from 2 data sets provided in a .txt file. The problem doesn’t occur while trying to read the file, but I guess when it tries to fill the 2 TH1f objects.
Try with “automatic bins”:
letturaFile("lens.txt", 40, 0., 0.)
That worked, I feel ashamed i overlooked something so simple 
Thank you for the help, you’ve been very helpful
(I had to answer today because of the number of posts per day)
This limit should disappear for you after a while. The number of posts per days seems limited for new users to avoid spamming.