GNU comes with a compiler called GCC. Originally this stood for "GNU C Compiler" but since it can now compile languages other than C it's name was changed to "GNU Compiler Collection". To check if you have GCC installed, type the following:
ciaran@pooh:~/book$ gcc --version
3.2.1
ciaran@pooh:~/book$
The version of GCC you have installed may be different, anything
similar, such as "2.95.2" or "3.3.0", is ok.
If you got an error message saying command not found
then you don't have GCC installed. If you installed GNU from a CD,
you should find GCC there. If you don't know how to install
applications from a CD then get a friend or the person who installed
your GNU system to do it for you.