[lifthrasiir]

Quantify "well known". Historically enough variation existed in this area [1], and C only happened to copy FORTRAN's behavior for the sake of compatibility.

[1] https://en.wikipedia.org/wiki/Modulo#In_programming_language...

[BlueTemplar]

Python does follow the convention, but what I am wondering now is why did FORTRAN break it ?

[asplake]

Fortran is old – 1958 onwards. It has precedence here, though at what point it separated the two behaviours into mod and modulo functions I don’t know.

Edit: From what I can tell, standardised in Fortran 90, presumably older than that.

[BlueTemplar]

My point is that Fortran doesn't have precedence on math, see this comment by Austin Feller :

http://python-history.blogspot.com/2010/08/why-pythons-integ...

[wombatpm]

Maybe because FORTRAN arrays index from 1 by default?