I learned a lot about programming by taking a book like this that was written specifically for the TRS-80 (which I did not own), and translating the programs to what I owned instead, which was a Sinclair ZX80. This primarily involved translating between different flavors of BASIC, but also deciding what I could arrange to leave out and still have an interesting game, due to the relatively constrained resources of my machine. Excellent experience.
I learned a lot about programming by taking this book and, since I didn't own a computer, figuring out how the code could produce the example listing. That's where I learned things like, to swap the values of two variables, you copy one to a third variable temporarily. I learned a ton of patterns like that.
Eventually I got my VIC-20, then an Apple ][, then an Amiga.
