[Resolved] ++ ?

Sayian

Ive tried to search google , but im not really sure what im searching for ..

In PHP code when someone use's the ++ what does that mean? and what does that do?

usally i see it as like i++ or somthing along those lines ..

Could someone explain to me what this is?

planetsim

http://www.php.net/manual/en/language.operators.increment.php I think just about sums it up.

Sayian

Ok im totally lost here.

When you assign a variable a value , like in this example from the php manual.

<?php
echo "<h3>Postincrement</h3>";
$a = 5;
echo "Should be 5: " . $a++ . "<br />\n";
echo "Should be 6: " . $a . "<br />\n";

Doesnt the variable hold the same value..

A = 5 , but in this example a++ equals 5 and a equals 6 ...... extremly confused ..

wad

Don't worry about being confused. You just need it better explained.

Basically, how it explains the $a++ is, you have 5. It tells you it has 5 in the first line, and then increments it by 1, making it 6. Then, on the second line, the variable $a has been changed to 6.

Another way to look at it, is this:

<?php
$a = 5;

echo "Should be 5: ". $a ."<br />";
$a += 1; // or $a = $a + 1;
echo "Should be 6: ". $a ."<br />";
?>

The ++ AFTER the $a indicates it carries out the addition function after it outputs the variable. Same goes for the -- operator.

When the ++ or -- is BEFORE the $a, it will carry out the addition or subtraction, and then return the variable.

Hope that clears things up some.

Sayian

But why is this needed? I understand a little more , but am not fully understanding the principle behind this .. when would this be used? and for why?

mrhappiness

because programmers are lazy...
$a++ is way shorter than $a = $a + 1

and:
it looks more sophisticated 😉

Installer

It was invented by Ken Thompson over 35 years ago for his B Language (post-dubbed "C without types"), largely to conserve compiler steps, clock cycles, and memory, back when such conservation was very important. It's been incorporated into many, if not most, languages developed since, even retro-fitted to some older ones.

Today it's used mainly because it's handy for saving an extra line of code, for less typing, and because it's fairly easy to read (among more technical reasons).

Where is it used? Wherever it fits. Why is it used? Because it's convenient and it works.

MikeSnead

It's great in for loops! :p


for ( $i = 0 ; $i < LIMIT ; $i++ )
{
     blah(blah[$i]);
}

thorpe

lets get the confusion pumping..... when you get your head around $i++, you've also got $i-- to deal with.

Installer

Then after that we can move on to <<, >>, ==, ===, &&, and ||.

laserlight

Well, at least there's no operator overloading in PHP.

Sayian

Ok , im new to php , but im not foolish. I catch on pretty quick , so tell me if i have this right ..

<?

$var = 27;
$month = febuary;

if( $month == "febuary") {
$var = $var++
}
echo " Their are " . $var . " Days in " . $month;

?>

Dont laugh if i got this wrong , only been with php for 3 weeks.

Installer

We're laughing, but only because you got it wrong. 😃

$var = $var++ 
// Would be just:
$var++;

Sayian

so if i need to use a ++ operator , i dont have to re-assign the variable?

$var = $var++

would have the same outcome as just

$var++

laserlight

Basically,
$var = $var++;
is equivalent to:
$var = $var;
$var = $var + 1;

So you might as well use:
$var++;
since that is equivalent to:
$var = $var + 1;

You could use:
++$var;
as well, as it would also be equivalent to:
$var = $var + 1;

But
$var = ++$var;
should be equivalent to:
$var = $var + 1;
$var = $var;

Of course, there is also:
$var = ++$var + $var++;

But I suggest staying away from such complex expressions that use side effects - in fact the C++ equivalent is undefined, and offhand I have no idea what PHP will do.

Installer

Well, I may have confused you on that one. With

$var = 1;
$x = $var++;
echo $x . '<br />';

you'll get "1". With

$var = 1;
$x = ++$var;
echo $x . '<br />';

you'll get "2". That's the difference between pre- and post-increment. One makes the change after the expression is evaluated, the other before.

justsomeone

You can think of $var++ as exactly the same as $var = $var + 1;

They both mean "Increment the value of $var by 1".

But you can also use the ++ version in interesting ways:

so:

$var=5;
// $var now has a value of 5;

echo ($var++);
// This will echo 5, then increment the value of $var by 1 to 6.

echo (++$var);
//This will increment the value of $var by 1 to 7, and then echo it

Installer

You can think of $var++ as exactly the same as $var = $var + 1;

Well, not exactly. A simplistic example:

// echos 1:
$var = 1;
$x = $var++;
echo $x . '<br />';

// echos 2:
$var = 1;
$x = ($var = $var + 1);
echo $x . '<br />';

justsomeone

yep you're right.

If you're used to using the return values of addition operations (eg $x = $x + 1), you will see a difference.

That's why I went with "you can think of", rather than saying that they functioned exactly the same. It was just to help someone new to the idea to get their head around it.

I have to say, though, that after a fairly lengthy experience in software design and development, I've never had to use the $a = ($b = $c + $d) construct, and hope to continue in that line.

I have come up with if ($a = $b) in the past, but that's usually a typo. 🙂

Installer

a fairly lengthy experience in software design and development

I back out, bowing.