Increments, ++$a and $a++

PHP
1

I can’t figure this out…

They say ++X is a PRE increment,
and X++ is a POST increment,

But a PRE/POST on what? The output? Or what am i saying now… What does any of this mean?

Can someone show me a example of using ++$a vs $a++ where it WOULD MATTER?

Here is some stuff i was testing

<?php

$a = 2;
$a = $a- + 1; // It equals 1, why?
echo $a;


$b = 1;
$b++;	
echo $b; // 2

$c = 1;
++$c;	
echo $c; // 2

$d = 1;
--$d;	
echo $d; // 0

$e = 1;
$e--;
echo $e; // 0

echo '<hr />';

for ($i = 0; $i < 5; $i++)
echo $i; // 01234

echo '<hr />';

for ($i = 0; $i < 5; ++$i)
echo $i; // 01234

echo '<hr />';
2

Okay this kind of makes sense, I find it a little tricky :\

Trying to wrap my head around this:
The pre/post increment only makes a difference if the increment is incorporated inside another statement and determines whether the pre or post increment value will be used in that other statemen

3

Say you are stuck with a startup value for a loop and that value is 0 (such the first key a new array defaults to).

Lets say that your requirement is to echo out the number 1 in the first part of the loop, because having a human readable array makes more sense to people when it starts with 1.


$element_out_of_your_control = 0 ;

foreach( $rows as $row ) {
echo ++$element_out_of_your_control ;
// do stuff

}

instead of :


foreach( $rows as $row ) {
$element_out_of_your_control++ ;
echo $element_out_of_your_control ;
// do stuff

}

using ++$a increments it immediately, whereas $a++ shows the increment next time it is used, hence you often see it as the last line inside a loop.


$ctr = 1 ; // set your counter

foreach( $rows as $row ){

// do stuff

$ctr++ ;
}
4

It’s PRE/POST on the current statement. Doing the following yields different results:

$a = 1;
echo ++$a;

$b = 1;
echo $b++;

As for where it would matter is very generic. Maybe you want to echo a counter then increment it by one. So instead of doing:

echo $a;
++$a;

You could just do:

 echo $a++;

Most of the time you’ll just use the PRE increment, as this avoids the parser having to create a copy of the value before incrementing.

5

This is basic math, but it may make more sense if you space it consistently. What you wrote is identical to this:

<?php

$a = 2;
$a = $a - +1; //which is the same as $a = $a - 1; and $a=$a-1;
echo $a;

The +1 just reassures that the 1 is positive, which is always assumed and therefore unneeded.

6

Think of it this way:

PRE: Increments the variable immediately.
POST: Increments the variable after it has been used.

7

It is one of those things you should not dwell upon - but simply acccept.

Like zits, grey hairs and weight gain.

8

$a = 5;
$b = ++$a;

$a = 5;
$c = $a++;

In both cases $a ends up equal to 6. The pre/post increment affects the values of $b and $c since $b is assigned the value of $a after incrementing $a while $c is set the value of $a before it is incremented.

The pre/post increment only makes a difference if the increment is incorporated inside another statement and determines whether the pre or post increment value will be used in that other statement.