if (!0) means what?

[Adams-Blake Company]

Recently I made this mistake:

if (!0){
echo "I am true";
}
else {
echo "I am false";
}

It always evaluated to "true". What does (!0) equate to in plain language?
Why is it always true.

Al

"Adams-Blake Company" <atakeoutcanton@adams-blaketakeout.com> wrote in
message news:vsvu58f0s0hq9c@news20.forteinc.com...

> Recently I made this mistake:
>
> if (!0){
> echo "I am true";
> }
> else {
> echo "I am false";
> }
>
> It always evaluated to "true". What does (!0) equate to in plain language?
> Why is it always true.
>
> Al
>

Ones & Zeros, On or Off, True or False

!0 equates to not zero - which must then be 1 - or true

so, if (true) - is always true

[J0hn Sm1th]

Adams-Blake Company wrote:

> Recently I made this mistake:
>
> if (!0){
> echo "I am true";
> }
> else {
> echo "I am false";
> }
>
> It always evaluated to "true". What does (!0) equate to in plain language?
> Why is it always true.
>
> Al
>

Have a look at: [url]http://www.blueshoes.org/en/developer/php_cheat_sheet/[/url]

Looks like '0' always evaluates to false, so essentially you're just
returning 'not false' which is always true ;)

[Adams-Blake Company]

<xyzzy> wrote:

>
> "Adams-Blake Company" <atakeoutcanton@adams-blaketakeout.com> wrote in
> message news:vsvu58f0s0hq9c@news20.forteinc.com...

>> Recently I made this mistake:
>>
>> if (!0){
>> echo "I am true";
>> }
>> else {
>> echo "I am false";
>> }
>>
>> It always evaluated to "true". What does (!0) equate to in plain
>> language? Why is it always true.
>>
>> Al
>>

>
>
> Ones & Zeros, On or Off, True or False
>
> !0 equates to not zero - which must then be 1 - or true
>
> so, if (true) - is always true

I had not thought of it in that way.

Thanks. And thanks to the person who posted the URL to the Cheat Sheet. Very
helpful.

Al

[Chung Leong]

Not quite true. Boolean is a distinct type in PHP. ! is a boolean operator,
so 0 first get convert into boolean (to false), then the expression is
evaluated. The difference between 0 and false is illustrated by the
following examples:

// Example A
if (!"Bush") {
echo "I am true";
}
else {
echo "I am false";
}

// Example B
if ("Bush" == 0) {
echo "I am zero";
}
else {
echo "I am not zero";
}

Example A prints "I am false", because a non-empty string converts to true.
Example B on the other hand, prints "I am zero" because "Bush" converts to
0. Thus, we get the following logic:

false == 0
0 == "Bush"
false != "Bush"

In linear algebra I think you would say "PHP variables do not form a vector
space."

Uzytkownik <xyzzy> napisal w wiadomosci
news:NaadnYu0CvoVZ1KiRVn-vw@comcast.com...

>
> "Adams-Blake Company" <atakeoutcanton@adams-blaketakeout.com> wrote in
> message news:vsvu58f0s0hq9c@news20.forteinc.com...

> > Recently I made this mistake:
> >
> > if (!0){
> > echo "I am true";
> > }
> > else {
> > echo "I am false";
> > }
> >
> > It always evaluated to "true". What does (!0) equate to in plain

language?

> > Why is it always true.
> >
> > Al
> >

>
>
> Ones & Zeros, On or Off, True or False
>
> !0 equates to not zero - which must then be 1 - or true
>
> so, if (true) - is always true
>
>
>
>

"Chung Leong" <chernyshevsky@hotmail.com> wrote in message
news:CsidnY5G26w9hE2iRVn-sQ@comcast.com...

> Not quite true. Boolean is a distinct type in PHP. ! is a boolean

operator,

> so 0 first get convert into boolean (to false), then the expression is
> evaluated. The difference between 0 and false is illustrated by the
> following examples:
>
> // Example A
> if (!"Bush") {
> echo "I am true";
> }
> else {
> echo "I am false";
> }
>
> // Example B
> if ("Bush" == 0) {
> echo "I am zero";
> }
> else {
> echo "I am not zero";
> }
>
> Example A prints "I am false", because a non-empty string converts to

true.

> Example B on the other hand, prints "I am zero" because "Bush" converts to
> 0. Thus, we get the following logic:
>
> false == 0
> 0 == "Bush"
> false != "Bush"
>
> In linear algebra I think you would say "PHP variables do not form a

vector

> space."
>
> Uzytkownik <xyzzy> napisal w wiadomosci
> news:NaadnYu0CvoVZ1KiRVn-vw@comcast.com...

> >
> > "Adams-Blake Company" <atakeoutcanton@adams-blaketakeout.com> wrote in
> > message news:vsvu58f0s0hq9c@news20.forteinc.com...

> > > Recently I made this mistake:
> > >
> > > if (!0){
> > > echo "I am true";
> > > }
> > > else {
> > > echo "I am false";
> > > }
> > >
> > > It always evaluated to "true". What does (!0) equate to in plain

> language?

> > > Why is it always true.
> > >
> > > Al
> > >

> >
> >
> > Ones & Zeros, On or Off, True or False
> >
> > !0 equates to not zero - which must then be 1 - or true
> >
> > so, if (true) - is always true
> >

I disagree.
Yes, strings can evaluate to true and false if they are null or !null
However, zero is numeric until you convert it to Boolean by using the !

<?
$a = 0;

echo "a = $a\n";
echo "!a = " . !$a . "\n";
echo "is_bool(a) ".($a ? "true":"false") . "\n";
echo "is_bool(!a) ".(!$a ? "true":"false") . "\n";
?>

*** produces ***

a = 0
!a = 1
is_bool(a) =false
is_bool(!a) =true