It was pretty common to distribute code as "listing" like this. Typically it came with a checksum for every line and a small program to compute and print that for your own program that you had typed over, which you could then use to fairly quickly(-ish) spot any typos.
All of this is how I learned to program by the way. Kids these days don't know how easy they have it.
All of this is how I learned to program by the way. Kids these days don't know how easy they have it.