Difference between if () { } and if () : endif;

They are the same but the second one is great if you have MVC in your code and don't want to have a lot of echos in your code. For example, in my .phtml files (Zend Framework) I will write something like this:

<?php if($this->value): ?>
Hello
<?php elseif($this->asd): ?>
Your name is: <?= $this->name ?>
<?php else: ?>
You don't have a name.
<?php endif; ?>

At our company, the preferred way for handling HTML is:

<? if($condition) { ?>
   HTML content here
<? } else { ?>
   Other HTML content here
<? } ?>

In the end, it really is a matter of choosing one and sticking with it.

Here's where you can find it in the official documentation: PHP: Alternative syntax for control structures

I think that it really depends on your personal coding style. If you're used to C++, Javascript, etc., you might feel more comfortable using the {} syntax. If you're used to Visual Basic, you might want to use the if : endif; syntax.

I'm not sure one can definitively say one is easier to read than the other - it's personal preference. I usually do something like this:

<?php
if ($foo) { ?>
   <p>Foo!</p><?php
} else { ?>
   <p>Bar!</p><?php
}  // if-else ($foo) ?>

Whether that's easier to read than:

<?php
if ($foo): ?>
   <p>Foo!</p><?php
else: ?>
   <p>Bar!</p><?php
endif; ?>

is a matter of opinion. I can see why some would feel the 2nd way is easier - but only if you haven't been programming in Javascript and C++ all your life. :)

I would use the first option if at all possible, regardless of the new option. The syntax is standard and everyone knows it. It's also backwards compatible.

Both are the same.

But: If you want to use PHP as your templating language in your view files(the V of MVC) you can use this alternate syntax to distinguish between php code written to implement business-logic (Controller and Model parts of MVC) and gui-logic. Of course it is not mandatory and you can use what ever syntax you like.

ZF uses that approach.

There is no technical difference between the two syntaxes. The alternative syntax is not new; it was supported at least as far back as PHP 4, and perhaps even earlier.

You might prefer the alternative form because it explicitly states which control structure is ending: endwhile, for example, can only terminate a while block, whereas if you encounter a brace, it could be closing anything.

You might prefer the traditional syntax, though, if you use an editor that has special support for braces in other C-like syntaxes. Vim, for example, supports several keystrokes for navigating to matching braces and to the starts and ends of brace-delimited blocks. The alternative syntax would break that editor feature.

I used to use the curly braces but now a days I prefer to use this short-hand alternative syntax because of code readability and accessibility.

Personally I prefer making it in two seperate sections but within the same PHP like:

<?php 
    if (question1) { $variable_1 = somehtml; }
    else { $variable_1 = someotherhtml; } 

    if (question2) {
        $variable_2 = somehtml2;
    }

    else { 
        $variable_2 = someotherhtml2;
    }         

etc.
$output=<<<HERE
htmlhtmlhtml$variable1htmlhtmlhtml$varianble2htmletcetcetc
HERE;
echo $output;

?>

But maybe it is slower?

I think it's a matter of preference. I personally use:

if($something){
       $execute_something;
}