Any mnemonic tip for boolean?

Question

I guess this is trivial for most of good¹ programmers, but I'm so used to programming using true and false² that when I encounter 0 and 1, I can never remember which one means true and which one means false.

Any suggestions?

¹Good: I mean one who knows C, of course :)
²I am a Java developer, as you have guessed ;)

score 9 · Answer 1 · answered Feb 16 '09 at 19:14

9

The mnemonic is "how much truth is in this?" Zero integer means zero truth. Anything else is nonzero truth. :)

answered Feb 16 '09 at 19:14

chaos

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Indeed, note the "anything nonzero is truth"! Anything nonzero is usually interpreted as `true`. – onnodb Feb 16 '09 at 19:17
Ah, but in some languages, -1 is also true. How can you have negative truth? – Adam Davis Feb 16 '09 at 19:19
The same way you can have 27 or [1,5] or "falsehood\n" truth: magic. – chaos Feb 16 '09 at 21:20
Also: 'some languages'? Are there any languages that allow interpretation of an arbitrary value in boolean context where -1 *isn't* true? – chaos Feb 16 '09 at 21:22
"At least one sheep in Scotland is black on one side" - I don't know every single language, therefore I cannot say "every" or even "most" so some is the safest term. – Adam Davis Feb 16 '09 at 23:11
Seems a little sheepish to me. – chaos Feb 16 '09 at 23:28
Would it blow your mind if I pointed out that this is not a mnemonic? :) – Lightness Races in Orbit Feb 20 '11 at 18:59
@Tomalak Geret'kal: I dunno, would it blow your mind to find out that "mnemonic device" means "trick for aiding memory" and is not actually limited to retarded nursery rhymes that form initialisms? – chaos Feb 20 '11 at 19:05

score 4 · Answer 2 · answered Feb 16 '09 at 19:19

4

I have a co-worker who simply has a Post-It note on his wall beside his desk:

False = 0
True != 0

answered Feb 16 '09 at 19:19

Rob Kennedy

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score 4 · Answer 3 · answered Feb 16 '09 at 19:43

4

If you are really having that much trouble with it, I would use the language to abstract it away.

e.g. in C

#define TRUE 1
#define FALSE 0

In general I would avoid having constants lying around in code anyways.

Consider,

if(my_var == TRUE)

as opposed to,

if(my_var == 1)

Though, here again you need to make sure you are testing for the right thing,

if(my_var != FALSE)

will catch more cases.

Cheers!

Christian

answered Feb 16 '09 at 19:43

tremoloqui

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Never test for true or false using a comparison operator. That's redundant and sometimes error-prone. Use "if(my_var)" instead. – David Thornley Feb 16 '09 at 21:20

score 3 · Answer 4 · answered Feb 16 '09 at 19:22

3

"Oh No!"
(Oh == 0)

answered Feb 16 '09 at 19:22

abyx

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score 3 · Answer 5 · answered Feb 16 '09 at 19:35

3

This is complicated by the fact that in the shell (sh, bash) true is 0 and false is 1:

$ true
$ echo $?
0
$ false
$ echo $?
1

answered Feb 16 '09 at 19:35

starblue

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that's because there's only one 0 and only one successful outcome, but there are as possible errors as there are positive return codes :) – Feb 16 '09 at 19:51
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in shells i don't think of return codes as true/false, rather as error code. obviously 0 means no error. – Javier Feb 16 '09 at 20:28
They can be used in conditional statements, so they are as boolean as are integers in C. – starblue Feb 16 '09 at 20:51
These aren't booleans per se. They're return codes. It's not the same. – Lightness Races in Orbit Feb 20 '11 at 19:00

score 3 · Accepted Answer · answered Feb 16 '09 at 19:59

3

Haven't you ever noticed that everyday items' power switches use a circle for off, and a line for on?

It's not much of a jump to link them up.

Off = circle = zero = false

On = line = one = true

answered Feb 16 '09 at 19:59

Imbue

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Yeah, use something like a closed circuit to indicate off, and something like an open circuit to indicate on. Who thought up that standard? – David Thornley Feb 16 '09 at 21:22

score 2 · Answer 7 · answered Feb 16 '09 at 19:14

2

Remember "nothing == false", "something == true"

answered Feb 16 '09 at 19:14

dwc

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Adam Davis · Answer 8 · 2009-02-16T19:26:14.280

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No mnemonic - and it gets even more complex if you come from a hardware background. But for programmers, just ask the question:

Is any bit set?

The answer is either true or false, and is the result. Only 0 (even in signed integers) has no bits set.

-Adam

edited Feb 16 '09 at 19:26

answered Feb 16 '09 at 19:17

Adam Davis

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Except for the old ones-compliment machines! I remember tracing a bug on a CDC-Cyber mainframe in school when ALL the conditions were true making all the bits 1 which is the 2nd representation for 0! – n8wrl Feb 16 '09 at 19:47
Ouch! One's complement machines leave me shivering. On the other hand, I never did like how unbalanced twos complement is - how the negative numbers always got one more than the positive numbers. It's like a tug of war where the bad guys always win by just a little bit... – Adam Davis Feb 16 '09 at 20:43

score 1 · Answer 9 · answered Feb 16 '09 at 19:13

1

Map both to On and Off. I think most programmers would map both sets the same way: 1/true both going to 'On', while 0/false both go to 'Off'.

answered Feb 16 '09 at 19:13

Joel Coehoorn

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score 1 · Answer 10 · answered Feb 16 '09 at 20:47

It depends on the language.

C: ( 0 ? "never happens" : "false") and ( 1 ? "true" : "never happens")
Ruby, ELisp: both 0 and 1 are true
bash (or cmd.exe): the true command (from coreutils) exits with a 0 status code and the false command exits with a non-zero status code

Many modern popular programming languages have strong C heritage therefore they consider 0 to be false and 1 (or any non-zero numbers) to be true.

Don't use mnemonics for boolean, use your language's idioms to test trueness.

score 0 · Answer 11 · answered Feb 16 '09 at 19:38

0

love c - because you can't multiply lies. :)

answered Feb 16 '09 at 19:38

Avram

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Any mnemonic tip for boolean?

11 Answers11