assigning variables in e.g. an if ....

[jodleren]

Hi

I have been looking into php.net, but could not find any proper
description.
There is a way of assigning variables from functions, while at the
same time using them in e.g. an if.
I have tried to use this, but failed.... and I have not found any
proper information about this?

E.g., if I am right, then

if(strpos($line , '='))

could be

if( ($i=strpos($lin e, '=')) !== false )
echo $i;

but just how does this work? the parantheses do it?
I asume I have to understand that as a statement in a statement?

WBR
Sonnich

[Geoff Berrow]

Re: assigning variables in e.g. an if ....

Message-ID:
<5f0aa7b8-0fe4-4b34-8f81-f288cb0aebec@59 g2000hsb.google groups.comfrom
jodleren contained the following:

>I have tried to use this, but failed.... and I have not found any
>proper information about this?
>
>E.g., if I am right, then
>
if(strpos($line , '='))
>
>could be
>
if( ($i=strpos($lin e, '=')) !== false )
echo $i;
>
>but just how does this work? the parantheses do it?
>I asume I have to understand that as a statement in a statement?

Not sure I understand your question. AIUI parentheses work the same way
they do in mathematics, ie the code inside is evaluated first. The
manual tells you what a function returns (note: some functions don't
return anything more meaningful than true or false). That value can be
assigned to a variable.

Now the manual entry for strpos is this
"Returns the position as an integer. If needle is not found, strpos()
will return boolean FALSE." Note the warning, if the character being
searched for is at the beginning of the string it could return 0, or in
other words a non-boolean false.

So in the first example the 'if' will be executed if the character is
found,as long as the character is not at position 0. To check for that
you'd need

if(strpos($line , '=')!==false)

In the second example the bit in parentheses is evaluated first
$i=strpos($line , '=')

$i now contains the output of strpos, an integer if the character is
found, false if not.

So now the parentheses have been evaluated we effectively have:

if( $i !== false )
echo $i;

in other words $i will be echoed as long as it is not false.








--
Geoff Berrow 011000100110110 0010000000110
001101101011011 001000110111101 100111001011
100110001101101 111001011100111 010101101011
http://slipperyhill.co.uk - http://4theweb.co.uk

[Bill H]

Re: assigning variables in e.g. an if ....

On Sep 25, 4:25 am, Geoff Berrow <blthe...@ckdog .co.ukwrote:

Message-ID:
<5f0aa7b8-0fe4-4b34-8f81-f288cb0ae...@59 g2000hsb.google groups.comfrom
jodleren contained the following:
>

I have tried to use this, but failed.... and I have not found any
proper information about this?

>

E.g., if I am right, then

>

 if(strpos($line , '='))

>

could be

>

 if( ($i=strpos($lin e, '='))  !== false )
   echo $i;

>

but just how does this work? the parantheses do it?
I asume I have to understand that as a statement in a statement?

>
Not sure I understand your question.  AIUI parentheses work the same way
they do in mathematics, ie the code inside is evaluated first.  The
manual tells you what a function returns (note: some functions don't
return anything more meaningful than true or false).  That value can be
assigned to a variable.
>
Now the manual entry for strpos is this
"Returns the position as an integer. If needle is not found, strpos()
will return boolean FALSE." Note the warning, if the character being
searched for is at the beginning of the string it could return 0, or in
other words a non-boolean false.
>
So in the first example the 'if' will be executed if the character is
found,as long as the character is not at position 0. To check for that
you'd need
>
 if(strpos($line , '=')!==false)
>
In the second example the bit in parentheses is evaluated first
$i=strpos($line , '=')
>
$i now contains the output of strpos, an integer if the character is
found, false if not.
>
So now the parentheses have been evaluated we effectively have:
>
if( $i  !== false )
 echo $i;
>
in other words $i will be echoed as long as it is not false.
>
--
Geoff Berrow  011000100110110 0010000000110
001101101011011 001000110111101 100111001011
100110001101101 111001011100111 010101101011htt p://slipperyhill.co .uk-http://4theweb.co.uk

It appears he is trying to do variable assignment inside the if ()
statement. Is this allowed? I now in actionscript this is not allowed,
and I believe in perl it is allowed and always returns true (could be
wrong there).

If so (or even if not) does a variable assignment return a true /
false value?

Bill H

[Gordon]

Re: assigning variables in e.g. an if ....

On Sep 25, 10:30 am, Bill H <b...@ts1000.us wrote:

On Sep 25, 4:25 am, Geoff Berrow <blthe...@ckdog .co.ukwrote:
>
>
>

Message-ID:
<5f0aa7b8-0fe4-4b34-8f81-f288cb0ae...@59 g2000hsb.google groups.comfrom
jodleren contained the following:

>

>I have tried to use this, but failed.... and I have not found any
>proper information about this?

>

>E.g., if I am right, then

>

 if(strpos($line , '='))

>

>could be

>

 if( ($i=strpos($lin e, '='))  !== false )
   echo $i;

>

>but just how does this work? the parantheses do it?
>I asume I have to understand that as a statement in a statement?

>

Not sure I understand your question.  AIUI parentheses work the same way
they do in mathematics, ie the code inside is evaluated first.  The
manual tells you what a function returns (note: some functions don't
return anything more meaningful than true or false).  That value can be
assigned to a variable.

>

Now the manual entry for strpos is this
"Returns the position as an integer. If needle is not found, strpos()
will return boolean FALSE." Note the warning, if the character being
searched for is at the beginning of the string it could return 0, or in
other words a non-boolean false.

>

So in the first example the 'if' will be executed if the character is
found,as long as the character is not at position 0. To check for that
you'd need

>

 if(strpos($line , '=')!==false)

>

In the second example the bit in parentheses is evaluated first
$i=strpos($line , '=')

>

$i now contains the output of strpos, an integer if the character is
found, false if not.

>

So now the parentheses have been evaluated we effectively have:

>

if( $i  !== false )
 echo $i;

>

in other words $i will be echoed as long as it is not false.

>

--
Geoff Berrow  011000100110110 0010000000110
001101101011011 001000110111101 100111001011
100110001101101 111001011100111 010101101011htt p://slipperyhill.co .uk-http://4theweb.co.uk

>
It appears he is trying to do variable assignment inside the if ()
statement. Is this allowed? I now in actionscript this is not allowed,
and I believe in perl it is allowed and always returns true (could be
wrong there).
>
If so (or even if not) does a variable assignment return a true /
false value?
>
Bill H

As with most languages that have C as a comm,on ancestor, assigning
within an IF is perfectly legal in PHP. I tend to use it a lot in
places where calling functions that can fail. For example:

if ($fileHandle = fopen ('/foo/bar/bax.txt'))
{
//...
fclose ($fileHandle)
}
else
{
// Error handler goes here
}

[Geoff Berrow]

Re: assigning variables in e.g. an if ....

Message-ID:
<10565497-9cda-4996-801e-ddf4811b0acb@e3 9g2000hsf.googl egroups.comfrom
Gordon contained the following:

>As with most languages that have C as a comm,on ancestor, assigning
>within an IF is perfectly legal in PHP.

And also very useful in while

while($row=mysq l_fetch assoc($result)) {

}
--
Geoff Berrow 011000100110110 0010000000110
001101101011011 001000110111101 100111001011
100110001101101 111001011100111 010101101011
http://slipperyhill.co.uk - http://4theweb.co.uk

[mijn naam]

Re: assigning variables in e.g. an if ....

"Bill H" <bill@ts1000.us schreef in bericht
news:671de5e5-9460-4bec-ae97-793a4e6fbc9f@79 g2000hsk.google groups.com...

But where does the "true" / "false" come from? Wouldn't a variable
assignment always be "true", or does the true false come from the
value of the variable after it has been assigned?

Bill H



<?php

$a=10;
$b=20;

$a=$b=5;

echo "a=$a\n";
echo "b=$b\n";

?>

Both variables are set to 5. $a is not set to true.


Try this:

<?php

$a=0;

if ($b=$a) echo "1: true\n";
if (($b=$a)==TRUE) echo "2: true\n";
if (($b=$a)===TRUE ) echo "3: true\n";

if (!($b=$a)) echo "4: false\n";
if (($b=$a)==FALSE ) echo "5: false\n";
if (($b=$a)===FALS E) echo "6: false\n";

$a=1;

if ($b=$a) echo "7: true\n";
if (($b=$a)==TRUE) echo "8: true\n";
if (($b=$a)===TRUE ) echo "9: true\n";

if (!($b=$a)) echo "10: false\n";
if (($b=$a)==FALSE ) echo "11: false\n";
if (($b=$a)===FALS E) echo "12: false\n";
?>

4: false
5: false
7: true
8: true

[Jerry Stuckle]

Re: assigning variables in e.g. an if ....

jodleren wrote:

Hi
>
I have been looking into php.net, but could not find any proper
description.
There is a way of assigning variables from functions, while at the
same time using them in e.g. an if.
I have tried to use this, but failed.... and I have not found any
proper information about this?
>
E.g., if I am right, then
>
if(strpos($line , '='))
>
could be
>
if( ($i=strpos($lin e, '=')) !== false )
echo $i;
>
but just how does this work? the parantheses do it?
I asume I have to understand that as a statement in a statement?
>
WBR
Sonnich
>
>

Sure, it works fine. The secret is that PHP, like C, C++ and Java,
treat the assignment operation ("=") as an operator. That is, $a=$b is
an expression, just as $a+$b is, and returns a value. In the case of
$a+$b, the returned value is, of course, the sum of $a and $b. For
$a=$b, it is the value of $a after the assignment. It means that an
assignment expression can be used anywhere another expression can be
used, i.e.

func($c=$a+$b).

The only thing to be cautious about is that the "=" operator has very
low precedence, so it's best to always enclose an expression using it in
parens to prevent unexpected results (as you did in your example).

P.S. A statement is one or more expressions terminated by a semicolon.

$i=strpos($line , '=') // is an expression.

$i=strpos($line , '='); // is a statement.

A minor syntactical difference, but a major difference in operation.

--
=============== ===
Remove the "x" from my email address
Jerry Stuckle
JDS Computer Training Corp.
jstucklex@attgl obal.net
=============== ===

[=?UTF-8?B?SXbDoW4gU8OhbmNoZXogT3J0ZWdh?=]

Re: assigning variables in e.g. an if ....

Bill H wrote:

But where does the "true" / "false" come from? Wouldn't a variable
assignment always be "true", or does the true false come from the
value of the variable after it has been assigned?

The result of an assignment operation is the assigned value, which then gets
implicitly casted to a boolean value (because the 'if' construct expects a
boolean value).

--
----------------------------------
Iván Sánchez Ortega -ivan-algarroba-sanchezortega-punto-es-

Error 99: - CPU too tired to continue.