Editing C (programming language) (section)

==== Structures and Unix kernel re-write ====
At [[Version 4 Unix]], released in November 1973, the [[Unix]] [[kernel (operating system)|kernel]] was extensively re-implemented in C.<ref name="sigplan" /> By this time, the C language had acquired some powerful features such as <code>struct</code> types.

The [[C preprocessor|preprocessor]] was introduced around 1973 at the urging of [[Alan Snyder (computer scientist)|Alan Snyder]] and also in recognition of the usefulness of the file-inclusion mechanisms available in BCPL and [[PL/I]]. Its original version provided only included files and simple string replacements: <code>#include</code> and <code>#define</code> of parameterless macros. Soon after that, it was extended, mostly by [[Mike Lesk]] and then by John Reiser, to incorporate macros with arguments and [[conditional compilation]].<ref name="sigplan">{{harvtxt|Ritchie|1993}}</ref>

Unix was one of the first operating system kernels implemented in a language other than [[assembly language|assembly]]. Earlier instances include the [[Multics]] system (which was written in [[PL/I]]) and [[Master Control Program]] (MCP) for the [[Burroughs large systems|Burroughs B5000]] (which was written in [[ALGOL]]) in 1961. In around <!--Better?: {{Circa|1977}}--> 1977, Ritchie and [[Stephen C. Johnson]] made further changes to the language to facilitate [[Software portability|portability]] of the Unix operating system.  Johnson's [[Portable C Compiler]] served as the basis for several implementations of C on new platforms.<ref name="unixport">{{cite journal |last1=Johnson |first1=S. C. |author-link1=Stephen C. Johnson |last2=Ritchie |first2=D. M. |author-link2=Dennis Ritchie |title=Portability of C Programs and the UNIX System |journal=Bell System Tech. J. |year=1978 |volume=57 |issue=6 |pages=2021–2048 |doi=10.1002/j.1538-7305.1978.tb02141.x |citeseerx=10.1.1.138.35 |s2cid=17510065 |issn = 0005-8580 }} (Note: The PDF is an OCR scan of the original, and contains a rendering of "IBM 370" as "IBM 310".)</ref>