[tmoravec]

size_t has been in the C standard since C89. "for (int i = 0..." might have it's uses so it doesn't make sense to disallow it. But I'd argue that it's not really a common textbook way to iterate over an array.

[pcwalton]

The first example program that demonstrates arrays in The C Programming Language 2nd edition (page 22) uses signed integers for both the induction variable and the array length (the literal 10 becomes int).

[frumplestlatz]

The language has evolved significantly, and we’ve learned a lot about how to write safer C, since that was published in 1988.

[Maxatar]

From what I see, that book was published in 1988.