🚀 go-pugleaf

In article <1991Apr26.034205.27308@netcom.COM> mrs@netcom.COM (Morgan Schweers) writes:
>    Can someone confirm (preferably in a post, so my MBX doesn't flood)
>the truth/falsity of FORTRAN being the starter of 'I' as a generic loop
>variable?

I assume Fortran programmers used it because mathematicians used it.  Take
a look at most math books, and you'll see things like:

	  n
	-----
	\    \
	 >	formula using i
	/    /
	-----
	 i=0

Translated into Fortran, this is

	DO 10 I = 0,100
	  statements using I
     10 CONTINUE

Mathematicians seem to use only single-character names for things, making
extensive use of fonts, case and alphabetic ranges to denote categories.
i, j, and k are integral indexes; m and n are index limits; a, b, and c are
coefficiants; x, y, and z are real variables, C and K are constants; etc.
The original programmers were mathematicians, so it's not surprising that
they continued to use the same conventions.

>    Then when I finally took FORTRAN, I discovered a possible reason.  I've
>never seen it documented anywhere, so I was wondering if my conjecture was
>right.  Any opinions?  (*IF* you are lucky enough not to have programmed
>in FORTRAN at any time, it's loops were only allowed to be done with
>INTEGER variables, and it's INTEGERS were hardcoded.  I believe 'I' was
>the first integer, tho I don't remember too well after some 6+ years...

Actually, the rule was that by default, any variable whose name begins with
I through N (I think N was the last) is an integer, and the rest are reals.
Declarations are permitted to override this default for a particular
variable, and the IMPLICIT statement can be used to change the default
rule.

>    It's interesting to note, also, that the standard structure that I've
>seen people go through is 'I', then 'J', then ofttimes to 'T'.  Why?

I usually see K used after J.  Again, this just mimics what mathematicians
do.

I've always assumed that I is the default index because it is the initial
of the word "index".
--
Barry Margolin, Thinking Machines Corp.

barmar@think.com
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