C89 / C90

C89, also called C90 after its later ISO ratification, was the first standardized version of C, published in 1989 by ANSI. It established the core language and standard library that later versions built on, and remains the baseline that many embedded and legacy systems still target for maximum portability. Some features considered standard today, like // single-line comments or declaring variables anywhere in a block, were not part of this original standard.