Visual Basic Forum for Visual Basic Programmers VB

[DoobieKeebler]

(I think this qualifies as "off topic".)

Here's one that had me puzzled for the first few years I was programming. (I started programming back in '81 and have been a hobbyist ever since.) In an If statement, "=" is "equals", "<" is "less than", and ">" is "greater than". Simple stuff.

But "<=" is "less than or equal to" and ">=" is "greater than or equal to". So why is "<>" "not equal to"? In a way it's not. It's "less than or greater than".

There are three states of equality, as listed above: equal to, less than, and greater than. If it's less than or greater than then it cannot be equal to. So VB sees the test as "less than or greater than", it's just us programmers (note the proper use of the word "us") that see it as "not equal".

[P.T.A.M.]

In other languages it's != I think (in C, right?)... I guess they wanted to be original?
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No one is completely useless. They can at least be an example of what to avoid.

[dougthomas]

Hi,

Here's my pennyworth......

Taking Doobie's logic:

=< means Equal to or Less than
>= means Greater than or Equal to
= Means Equal to

it follows the <> must be Not Equal to

Think of:

If 3 =< 4 then...... 3 is less than 4 (True) or equal to 4 (False)
True Or False = True

If 4 >= 3 then...... 4 is greater than 3 (True) or equal to 3 (False)
True Or False = True

if 4 = 3 then......... (False) 4 doesn't equal 3
False = False

If 4 <> 3 then...... 4 is not less than 3 (False) or 4 is greater than 3 (True)
False Or True = True


Thinking about it, if a number is less than another number OR it's greater than that number then it can't possibly be equal to it !!

I think it was DeMorgan's Theory: A or B = NOT(A and B) and Not A or NOT B = NOT(A AND B) and if you play with that for long enough you can prove the above. (I can't but you may be able to !!)


QED !

Regards
Doug
PS In my day (early '70's) in Fortran it was .EQ.,.NE.,.GT.,.GE.,.LT.,.LE.)

[DoobieKeebler]

It's actually clever when you think of it. BASIC is one of the "prehistoric" languages created when memory was tight and you needed to code as efficiently as possible. If you already have a construct (not sure I'm using the right word here) that can handle two tokens, why create a unique token when you can pass the construct two tokens it can already deal with?

Since you go back that far Doug, you might know this. I've heard it but for me it was just trivia. What was the floppy disk size biger than 5.25"? 7 7/8" comes to mind but so many things come to mind that never were.

[dougthomas]

The early ones were 8 inch, then a "standard" of 5.25 inch appeared when Microcomputers "DOS" came along.

Also, Amdahl and later IBM (or the other way round) used 12 inch floppies for IMPL (Initial MicroProgram Load) for their Processors and Disc Controllers. Think I've got one or two somewhere, togehter with the Card Punch and platter of real Core Store from a KDF9 (suspect your parents weren't born when that was running !!)

Regards
Doug

[vbman995]

Hey, I still have a 5.25 inch floppy. It is the coolest thing ever! It is neat to know that at one time, that 5.25 floppy was the best technology that was around. Now we have thumb drive that hold upto 4 Gigs. (I think the max I have seen so far is 4 gigs.)

[DoobieKeebler]

Yeah, but that's 4GB before it's formatted, right?. My DVD+RW disc gives me 4.3GB formatted. One day this too shall be quaint. ("Grandpa, how did you ever get by with a 120GB hard drive? I'm gonna have to add another 100PB [pecabyte, 1,048,576 GB] drive soon.")
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"In theory, there's no difference between theory and practice. In practice, there is." -- Yogi Berra

[P.T.A.M.]

[dougthomas]

One of the first machines I worked on was an ICL 470, it had a "multiuser" operating system (called MultiJob) and we had 385Kb of memory for programs to run in. No Virtual storage - what you saw was what you got.The interactive bit was through ASR33 teletypes.

Even so we had 3 "streams", RIRO - you prog would load & run for a given time and then "roll-out" to let another one in, this went on in a circular fashion until your prog finished (it was nearly Virtual Memory, except you got dumped out to staging and then reloaded). Your prog had to be less than 64K though to qualify for RIRO. The other two were batch, one to support the printers and card and paper tape readers and the other for "Commercial" progs such as Payrolls and things. Backing storage was a mixture of removable disks. (8 Mb , 30Mb and 60Mb) and Tape Drives (800 bpi, 1600bpi and (later on) 6250bpi. We had enough tape to circumnavigate the Universe at least twice! The Operating system ran of one of the 8Mb disks. (and there was still space for a development system)

The compiler and linker technology was, IMHO, *very* advanced, programs would be segmented so that bits could be overlayed on each other to conserve memory and whilst "event driven code" wasn't known as such you had to write the code in a structured manner where you knew that a particular bit wasn't going to be used again so it could be overlayed with the next bit. If you take a standard model of a program, it is in 3 bits, input, processing and output. The first level of segmentation would be on each bit (once you've done all the input, you can overlay that with the processing and when that finished you could overlay that with the output, just have some "common areas" between each one to pass information.) Next level would be within the processing etc etc. Everything was reentrant and serially reusable as well. I used to write a lot of 370 Assembler routines for the Fortran community to keep storage down to a minimum, loads of self modifying code as well.

Ah, those were the days, then Virtual Memory came along and spoiled it all !!

Regards
Doug

[vbman995]

[dougthomas]

Hey, there's nothing wrong with the Commadore 64 I've got one in the attic together with the B/W TV I used to use it with.
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