From: krewat@kilonet.net (Arthur Krewat)
Subject: [TUHS] Array index history
Date: Wed, 7 Jun 2017 14:46:29 -0400 [thread overview]
Message-ID: <23afd785-e260-75ca-5c46-77c62fbcf3cd@kilonet.net> (raw)
In-Reply-To: <CAC20D2N+FqjYXBfqLtfEyNUecRFnYcySo_noP1XkdA=FN-nvYw@mail.gmail.com>
If you think of an array as a memory area of bytes, words, whatever, the
simple way to deal with it is the index being 0 is the first in the array.
Why go to the trouble of decrementing the index to retreive the first
entry?
ALGOL did indeed have arrays with bounds:
INTEGER ARRAY K,L[0:10,0:10];
Two arrays, K and L with 0 first, 10 last. Total of 11 elements.
Of course, it's a "higher level" language than C. My thinking on the
subject is that C is very close to assembler, so if you're using for
example Intel X86 instructions:
MOV SI,1
MOV AL,[SI + ARRAY1] ; retrieve the SECOND
element (byte)
Likewise, for words, just left-shift SI one bit.
For me having started out in assembler (actually, MACRO-10 on a PDP-10),
it's intuitive as to why/how C does arrays.
ak
next prev parent reply other threads:[~2017-06-07 18:46 UTC|newest]
Thread overview: 52+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <CAH_OBiewwwS6kbdWKUO-j3v=Do+Y9AzBn4ZkyVic7LOJN5WX7w@mail.gmail.com>
[not found] ` <CAH_OBid5q-YeB6UYeOfjW68s3nb3TX_icC5dFMapfo=7_q5DUQ@mail.gmail.com>
[not found] ` <CAH_OBideJeNGiiys=VOEYcU1cffSg+6zDOD39HOU74vumQF0kA@mail.gmail.com>
[not found] ` <CAH_OBie_+dQXOC2OaZii5K=j1Ljmv-OvAVXvyypoLJ10jaysWA@mail.gmail.com>
[not found] ` <CAH_OBidXd1Lpgp8ttM3sWLfXDT0ms5EGAzEjPH9QkY+bXyev2w@mail.gmail.com>
[not found] ` <CAH_OBifge2RrwcDvSV46gwLAc0wHVtH++gdMBhXi-x8C0a_2jw@mail.gmail.com>
[not found] ` <CAH_OBic3MTy-20C_T2ciT2x+EjNZvXR2PJ0OzB0qRp1gd2OL-g@mail.gmail.com>
2017-06-07 12:56 ` shawn wilson
2017-06-07 13:16 ` Ron Natalie
2017-06-07 13:20 ` arnold
2017-06-07 13:50 ` Michael Kjörling
2017-06-07 14:02 ` arnold
2017-06-08 11:28 ` Christian Neukirchen
2017-06-08 14:56 ` shawn wilson
2017-06-07 14:58 ` Tony Finch
2017-06-07 23:57 ` Dave Horsfall
2017-06-07 16:31 ` Lyndon Nerenberg
2017-06-08 0:47 ` Bakul Shah
2017-06-07 17:59 ` Tim Bradshaw
2017-06-07 18:29 ` Clem Cole
2017-06-07 18:46 ` Arthur Krewat [this message]
2017-06-07 19:03 ` Ron Natalie
2017-06-07 19:15 ` Arthur Krewat
2017-06-07 19:49 ` Ron Natalie
2017-06-08 1:58 ` ARJANEN Loïc Jean David
2017-06-08 13:49 ` Random832
2017-06-08 13:55 ` Arthur Krewat
2017-06-08 18:41 ` Tim Bradshaw
2017-06-08 2:45 ` Robert Swierczek
2017-06-08 4:05 ` Dave Horsfall
2017-06-08 6:19 ` Peter Jeremy
2017-06-08 7:02 ` Dave Horsfall
2017-06-08 13:53 ` Ron Natalie
2017-06-08 2:27 Doug McIlroy
2017-06-08 12:49 ` William Cheswick
2017-06-08 12:56 ` Michael Kjörling
2017-06-08 13:45 ` Dan Cross
2017-06-08 13:57 ` Ron Natalie
2017-06-10 21:08 ` Nemo
2017-06-08 15:04 ` Dave Horsfall
2017-06-08 15:09 ` William Pechter
2017-06-08 16:53 ` Steve Nickolas
2017-06-08 20:17 ` Larry McVoy
2017-06-09 0:03 ` Greg 'groggy' Lehey
2017-06-08 9:16 Richard Tobin
[not found] <mailman.882.1496854900.3779.tuhs@minnie.tuhs.org>
2017-06-08 18:20 ` David
2017-06-08 18:55 ` Ron Natalie
2017-06-09 21:21 ` Steve Johnson
2017-06-09 21:52 ` Arthur Krewat
2017-06-08 22:29 ` Johnny Billquist
2017-06-08 23:16 ` Ron Natalie
2017-06-08 23:41 ` Steve Nickolas
2017-06-09 15:12 ` Random832
2017-06-09 16:30 ` Ron Natalie
2017-06-09 0:21 ` Johnny Billquist
2017-06-09 0:25 ` Pete Turnbull
2017-06-09 1:19 ` Toby Thain
2017-06-09 2:14 ` Pete Turnbull
[not found] <mailman.890.1496953026.3779.tuhs@minnie.tuhs.org>
2017-06-08 22:28 ` Johnny Billquist
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