I tried to print the result in C-ish format like in the tutorial.
I got the following error.

Parameter no longer used.  See GPTree.java for details.
PARAMETER: pop.subpop.0.species.ind.tree.0.c
     ALSO: gp.tree.c
SYSTEM EXITING FROM ERRORS

Just thought I should put it up.
Maybe the tutorial is out of date and doesn't work
with the new ECJ version?