[creativecoding]

I was wondering why this is happening.

code:

<?php
$page = (isset($_GET['page'])) ? $_GET['page'] : 0;
echo '<a href="?page=' . $page+1 . '" class="pull-right" class="button pull-right">Next</a><br>';
echo '<a href="?page=' . ($page+1) . '" class="pull-right" class="button pull-right">Next</a>';
?>

Output:

1" class="pull-right" class="button pull-right">Next</a><br>
<a href="?page=1" class="pull-right" class="button pull-right">Next</a>

I'm using WAMP and PHP 5.3

This post has been edited by creativecoding: 08 April 2012 - 04:55 PM

[Duckington]

Well the "how" would be because in the first line you don't have $page+1 in a set of ()

Not sure on the why though, other than it clearly doesn't like you trying to add like that within a concatenation.

[hiddenghost]

Concatenation has precedence over the addition operator.

So it's trying to concatenate a variable that is probably equal to 0 that also has a plus sign next to it.

It's probably the plus sign because it's not evaluating after the concatenation so the code fouls up because a number is not able to sum to a string.

This post has been edited by hiddenghost: 08 April 2012 - 05:12 PM

[Atli]

The + and . operators have equal precedence, so when you order them like that they are evaluated left to right. Which means that the first . concats the first string and the $page value. Then the + adds the string -- which when used in an arithmetic operation will be converted to 0 -- to the 1, after which it finally concats the output of that addition to the string on the end.

[creativecoding]

Very good explanation, Atli.

[CTphpnwb]

I think there may be a little more to this than the order of operations. Check this out:

<?php
$x = 10;
echo 'testing: '. $x + 2 .'<br>';
echo 'testing: '.($x+2).'<br>';
?>

Output is missing the first testing:

2<br>testing: 12<br>

And this way just gets an error:

<?php
$x = 10;
echo 'testing: '.$x + 2.'<br>';
echo 'testing: '.($x+2).'<br>';
?>

[08-Apr-2012 21:59:01] PHP Parse error:  syntax error, unexpected T_CONSTANT_ENCAPSED_STRING, expecting ',' or ';' in /Users/me/Documents/htdocs/test.php on line 3

[Atli]

CTphpnwb, on 09 April 2012 - 02:00 AM, said:

Output is missing the first testing:

That's because the first 'testing', along with the $x variable, are converted into a 0 for the arithmetic operation done when the + operator is applied.

Try starting the first 'testing' with a number. Then, instead of being converted to a 0 and appearing to disappear completely, it will be converted into that number and you'll get that number + 2 instead of just 2.

CTphpnwb, on 09 April 2012 - 02:00 AM, said:

And this way just gets an error:

This would be because the . that you mean to be a concat operator is now read as if it were separating the 2 from a fraction. Try:

echo 'testing: '. $x + 2.0.'<br>';

[CTphpnwb]

I knew there was a reason I always prefer to use parentheses: being explicit saves hassle.

[hiddenghost]

Atli, on 08 April 2012 - 07:12 PM, said:

The + and . operators have equal precedence, so when you order them like that they are evaluated left to right. Which means that the first . concats the first string and the $page value. Then the + adds the string -- which when used in an arithmetic operation will be converted to 0 -- to the 1, after which it finally concats the output of that addition to the string on the end.

Oh your right. I looked it up again.
Whoops! Thanks for clarifying that.

[Atli]

CTphpnwb said:

I knew there was a reason I always prefer to use parentheses: being explicit saves hassle.

Yea, very true. I also find it a lot more readable with the parenthesis.

Although when I'm dealing with an echo statement like that, I'd be much more likely to pass things as multiple parameters rather than a single, concatenated string:

echo 'testing: ', $x + 2, '<br>';

Either that, or simply:

$x = 10;
$x2 = $x + 2;
echo "testing: {$x2}<br>";

Separation of presentation and logic, right!

[hiddenghost]

You know it's strange I have never really payed too much attention to type differences when it comes to strings and numbers.
Yet I don't think I have ever had this issue with echo.

Actually the way I code is kind of haphazard so I get into quite a bit of trouble. Just not that one problem.

Come to think of it I almost never use php type casting. Is that good or bad?

[hiddenghost]

Atli, on 08 April 2012 - 09:42 PM, said:

Either that, or simply:

$x = 10;
$x2 = $x + 2;
echo "testing: {$x2}<br>";

Separation of presentation and logic, right!

That's the way I do it. I don't ever use the comma way in echoes. Just personal consistency I guess.

What about?

$x = 10;
$x += 2;
echo "testing: $x<br>";
// or echo "testing: {$x}<br>";
// or
echo preg_replace("/\[num\]/", $x, "testing: [num]<br>");

Sorry, got a little silly there.

[CTphpnwb]

Atli, on 08 April 2012 - 10:42 PM, said:

Separation of presentation and logic, right!

Ah! Another reason I'd be unlikely to see this is that I'm more likely to be doing something like:

$x = 10;
echo str_replace("{sum}", $x+2, file_get_contents("somefile.html"));

[Dormilich]

CTphpnwb, on 09 April 2012 - 03:39 PM, said:

Ah! Another reason I'd be unlikely to see this is that I'm more likely to be doing something like:

$x = 10;
echo str_replace("{sum}", $x+2, file_get_contents("somefile.html"));

not to forget the printf() family of functions.