Xref: utzoo comp.lang.modula2:707 comp.lang.misc:1265 Path: utzoo!mnetor!uunet!husc6!cca!g-rh From: g-rh@cca.CCA.COM (Richard Harter) Newsgroups: comp.lang.modula2,comp.lang.misc Subject: Re: 0-based/1-based arrays Message-ID: <25739@cca.CCA.COM> Date: 19 Mar 88 16:58:25 GMT References: <7161@sol.ARPA> <2740@mmintl.UUCP> <4343@june.cs.washington.edu> <942@micomvax.UUCP> <1886@gumby.mips.COM> <9475@ism780c.UUCP> Reply-To: g-rh@CCA.CCA.COM.UUCP (Richard Harter) Organization: Computer Corp. of America, Cambridge, MA Lines: 39 In article <9475@ism780c.UUCP> darryl@ism780c.UUCP (Darryl Richman) writes: >In article <1886@gumby.mips.COM> uday@mips.COM (Uday Kurkure) writes: >> In Mathematics, zero means nothing, void. In computer science, zero >I'm not a math major, but 0 is not void. Void is null (e.g., the slashed >capital O). This is a very important distinction. Please, let us not confuse things. The word 'number' has different meanings in different contexts. This may be obscured by that fact one uses the same symbols and the same 'things' so to speak, but it is nonetheless true. A cardinal number is (or can be treated as) the measure of the size of a set. I.e. some sets have one element, some sets have two elements, and so on. [A set, for the totally non-mathematical, is a collection of things considered as a whole. The things in the collection are called elements of the set.] The void set, or empty set, is [the] set with no elements. Zero (0) is measure of the size of the void set. Cardinal numbers start with 0 and go 0,1,2,... An ordinal number is a specification of the position of an element in an ordered sequence. If I have a sequence, a is the first element, b is the second, and c is the third. An ordinal number is related to a cardinal number since the ordinal of the last element of the sequence is the 'same' as the cardinal measuring the size of the sequence, considered as a set. I.e., in a sequence with n elements the last one is the n'th. Ordinals start with 1, and go 1,2,3,... In arithmetic the numbers are primitive elements with arithmetic operations defined on them. Zero is the identity element, i.e. the number such that for all x, x+0 = x. It turns out that there is a direct correspondence between the non-negative integers of arithmetic and the cardinal numbers. And so on. Sorry to be pedantic, but what a number is and what it means depends on what you are talking about and what you mean. -- In the fields of Hell where the grass grows high Are the graves of dreams allowed to die. Richard Harter, SMDS Inc.