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!