From mboxrd@z Thu Jan  1 00:00:00 1970
From: krewat@kilonet.net (Arthur Krewat)
Date: Wed, 7 Jun 2017 14:46:29 -0400
Subject: [TUHS] Array index history
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Message-ID: <23afd785-e260-75ca-5c46-77c62fbcf3cd@kilonet.net>

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