To compile you need flex:
Debian/Ubuntu:
apt-get install flex

How it work:
$ make
$ ./gram file.c file1.h <...>
$ ls
file.c file.c_ file1.h file1.h_ convert.h gram
$ # file with '_' is obfuscated
$ # file convert.h have all obfuscation connections
$ # to compile 
$ gcc file.c_ file1.h convert.h -o file
$ ./file
Oh Yeah!

To test it:
$ ./gram arithmetique.c
$ ls
arithmetique.c arithmetique.c_ gram convert.h
$ gcc arithmetique.c_ convert.h -std=c99 -o test
$ ./test
Usage : ./a.out [nbr] [nbr]
$ # :D

That's all!