Hello, all.
Maurice wrote (paraphrased): ... but first I have to copy grx20.pas to the $DJDIR$ directory, or I need to add the option --unit-path=grx232/pascal to enable gpc to locate this file.
That was the key! The programs compile fine now.
I had also written about the new data types. I like the clean, systematic shortCard, medCard (sounds like what a doctor carries), and so on.
I'll note that the web page http://agnes.dida.physik.uni-essen.de/~gnu-pascal/gpc_73.html#SEC73 (7.2, data types) doesn't have a link to a page on reals, so I had to guess. But fortunately the reals seems to be systematic and similar to the integers.
Many thanks to all the comments and help I've received over the last week! No on to some actual programming!
Toby