What are the historical reasons C languages have pre-increments and post-increments?

Question

(Note: I am not asking about the definitions of pre-increment vs. post-increment, or how they are used in C/C++. Therefore, I do not think this is a duplicate question.)

Answer 1

The PDP-11 had a single instruction that corresponded to *p++, and another for *--p (or possibly the other way round).