At the time it was written, there was a good chance that the person reading it would not be doing so at a computer. Their computer access was quite likely via a terminal on a time sharing system, that they had to share with others. They couldn't hog a terminal while reading a book and typing in examples from it.
So books of that day where written so you could learn a lot just from reading the book and thinking seriously about the examples, and working out the exercises in your head or on paper
It helped if every couple of days or so you could get some computer time and try out the things you learned, but it wasn't actually necessary. In the case of K&R, you could go through the whole book without touching a computer, and then one or two sessions afterwards trying things out could be enough to correct your misunderstandings.
I wish more books were like that today. Nowadays, they assume you are a computer all the while you are reading the book, and often depend on that when writing the text.
So books of that day where written so you could learn a lot just from reading the book and thinking seriously about the examples, and working out the exercises in your head or on paper
It helped if every couple of days or so you could get some computer time and try out the things you learned, but it wasn't actually necessary. In the case of K&R, you could go through the whole book without touching a computer, and then one or two sessions afterwards trying things out could be enough to correct your misunderstandings.
I wish more books were like that today. Nowadays, they assume you are a computer all the while you are reading the book, and often depend on that when writing the text.