Arttırım ve Eksiltim İşleçleri

PHP, C tarzı önceden ve sonradan arttırım ve eksiltim işleçlerini destekler.

Bilginize: Arttırım ve eksiltim işleçleri sadece sayıları ve dizeleri etkiler. Diziler, nesneler, mantıksallar ve özkaynaklar etkilenmez. null değerini eksiltmenin bir etkisi yoktur fakat arttırmanın sonucu 1'dir.

Arttırım ve Eksiltim İşleçleri
Örnek İsim Etkisi
++$a Önceden arttırım $a bir arttırıldıktan sonra döndürülür.
$a++ Sonradan arttırım $a döndürüldükten sonra değeri bir arttırılır.
--$a Önceden eksiltim $a bir eksiltildikten sonra döndürülür.
$a-- Sonradan eksiltim $a döndürüldükten sonra değeri bir eksiltilir.

Basit bir betik örneği:

<?php
echo "<h3>Sonradan arttırım</h3>\n";
$a 5;
echo 
"5 olmalı: " $a++ . "<br />\n";
echo 
"6 olmalı: " $a "<br />\n";

echo 
"<h3>Önceden arttırım</h3>\n";
$a 5;
echo 
"6 olmalı: " . ++$a "<br />\n";
echo 
"6 olmalı: " $a "<br />\n";

echo 
"<h3>Sonradan eksiltim</h3>\n";
$a 5;
echo 
"5 olmalı: " $a-- . "<br />\n";
echo 
"4 olmalı: " $a "<br />\n";

echo 
"<h3>Önceden eksiltim</h3>\n";
$a 5;
echo 
"4 olmalı: " . --$a "<br />\n";
echo 
"4 olmalı: " $a "<br />\n";
?>

PHP, karakter değişkenleri üzerinde çalışırken C'nin değil Perl'in yöntemlerini izler. Örneğin, PHP ve Perl'de $a = 'Z'; $a++; ifadesi $a içinde 'AA' değerini döndürürken, C'de a = 'Z'; a++; ifadesi a içinde'[' döndürür. 'Z' için ASCII değer 90, '[' için 91'dir. Karakterlerin arttırılabileceğini fakat azaltılamayacağını ve sadece ASCII harflerin ve rakamların (a-z ve A-Z, 0-9) desteklendiğine dikkat ediniz. Diğer karakterler üzerinde arttırım ve eksiltim etkisiz olup özgün değer değişmeden döndürürlür.

Örnek 1 - Karakter değişkenleri üzerinde aritmetik işlemler

<?php
echo '== Harfler ==' PHP_EOL;
$i 'W';
for (
$n=0$n<6$n++) {
    echo ++
$s PHP_EOL;
}
// Rakam karakterleri farklı davranır
echo '== Rakamlar ==' PHP_EOL;
$d 'A8';
for (
$n=0$n<6$n++) {
    echo ++
$d PHP_EOL;
}
$d 'A08';
for (
$n=0$n<6$n++) {
    echo ++
$d PHP_EOL;
}
?>

Yukarıdaki örneğin çıktısı:

== Harfler ==
X
Y
Z
AA
AB
AC
== Rakamlar ==
A9
B0
B1
B2
B3
B4
A09
A10
A11
A12
A13
A14

Mantıksal değerlere arttırım ve eksiltim uygulamanın bir etkisi olmaz.

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User Contributed Notes 10 notes

up
59
hartmut at php dot net
11 years ago
Note that

$a="9D9"; var_dump(++$a);   => string(3) "9E0"

but counting onwards from there

$a="9E0"; var_dump(++$a);   => float(10)

this is due to "9E0" being interpreted as a string representation of the float constant 9E0 (or 9e0), and thus evalutes to 9 * 10^0 = 9 (in a float context)
up
5
aluciffer at hotmail dot com
9 years ago
Regarding character incrementing and PHP following Perl's convention with character operations.
Actually i found that there is a difference, and incrementing and decrementing unfortunately does not yield the reverse, expected results.
For example, the following piece of code:
<?php
echo '== Alphabets ==' . PHP_EOL;
$s = 'W';
for (
$n=0; $n<10; $n++) {
    echo ++
$s . ' ';
}
echo
PHP_EOL;

for (
$n=10; $n>0; $n--) {
    echo (--
$s) . ' ';
}
?>
Will output:
== Alphabets ==
X Y Z AA AB AC AD AE AF AG
AG AG AG AG AG AG AG AG AG AG

Please note that the decrement operator has no effect on the character or string.

On the other hand, in Perl, the similar script:

#!/usr/bin/perl

my $s = 'W';

foreach (1 .. 10) {
print  ++$s . " ";


print "\n";

foreach (1 .. 10) {
print --$s . " ";
}

Will output:

X Y Z AA AB AC AD AE AF AG
-1 -2 -3 -4 -5 -6 -7 -8 -9 -10
up
2
ayyappan dot ashok at gmail dot com
8 years ago
Rule for Increment and decrement:

At some moment we could be confused with increment and decrement in various cases. To avoid such cases, let us follow certain logical rule behind to get successful results with out mess.

<?php
           $n
= 3;
           echo
$n-- + --$n;
           echo
"<br/>";
           echo
$n;
?>

1. Postfix form of ++,-- operator follows the rule  [ use-then-change ],

2. Prefix form (++x,--x) follows the rule [ change-then-use ].

Solution based on the rule:

Step 1: 
use then change   $n--  use is 3 and change is 2

Step 2. 
change then use   --$n  change is 2 and use is 1

Step 3.
use + use = (3 + 1) = 4

Courtesy : stackoverflow : Sunil Dhillon : 4686665
up
4
dsbeam at gmail dot com
14 years ago
When using the ++ operator by itself on a variable, ++$var is faster than $var++ and uses slightly less memory (in my experiments).  It would seem like this could be optimized in the language during runtime (if $var++ is the only thing in the whole statement, it could be treated as ++$var).

I conducted many tests (I believe to be fair), and here's one of the results:

$i++ took 8.47515535355 seconds and 2360 bytes
++$i took 7.80081486702 seconds and 2160 bytes

Here's my code.  If anyone sees a bias in it, tell me.  I conducted it many times, each time going through a loop one million iterations and doing each test 10 - 15 times (10 - 15 million uses of the ++ operator).

<?php

ini_set
( 'MAX_EXEC_TIME', 120 );
ob_start( );

$num_tests = 10;
$startFirst = $startSecond = $endFirst = $endSecond = $startFirstMemory = $endFirstMemory = $startSecondMemory = $endSecondMemory = $someVal = 0;
$times = array( '$i++' => array( 'time' => 0, 'memory' => 0 ), '++$i' => array( 'total' => 0, 'memory' => 0 ) );

for(
$j = 0; $j < $num_tests; ++$j )
{
        for(
$i = 0, $startFirstMemory = memory_get_usage( ), $startFirst = microtime( true ); $i < 10000000; $i++ ){ $someval = 2; }
       
$endFirstMemory = memory_get_usage( );
       
$endFirst = microtime( true );

        for(
$i = 0, $startSecondMemory = memory_get_usage( ), $startSecond = microtime( true ); $i < 10000000; ++$i ){ $someval = 2; }
       
$endSecondMemory = memory_get_usage( );
       
$endSecond = microtime( true );

       
$times[ '$i++' ][ $j ] = array( 'startTime' => $startFirst, 'endTime' => $endFirst, 'startMemory' => $startFirstMemory, 'endMemory' => $endFirstMemory );
       
$times[ '++$i' ][ $j ] = array( 'startTime' => $startSecond, 'endTime' => $endSecond, 'startMemory' => $startSecondMemory, 'endMemory' => $endSecondMemory );
}

for(
$i = 0; $i < $num_tests; ++$i )
{
       
$times[ '$i++' ][ 'time' ] += ( $times[ '$i++' ][ $i ][ 'endTime' ] - $times[ '$i++' ][ $i ][ 'startTime' ] );
       
$times[ '++$i' ][ 'time' ] += ( $times[ '++$i' ][ $i ][ 'endTime' ] - $times[ '++$i' ][ $i ][ 'startTime' ] );
       
$times[ '$i++' ][ 'memory' ] += ( $times[ '$i++' ][ $i ][ 'endMemory' ] - $times[ '$i++' ][ $i ][ 'startMemory' ] );
       
$times[ '++$i' ][ 'memory' ] += ( $times[ '++$i' ][ $i ][ 'endMemory' ] - $times[ '++$i' ][ $i ][ 'startMemory' ] );
}

echo
'There were ' . $num_tests . ' tests conducted, here\'s the totals<br /><br />
$i++ took '
. $times[ '$i++' ][ 'time' ] . ' seconds and ' . $times[ '$i++' ][ 'memory' ] . ' bytes<br />
++$i took '
. $times[ '++$i' ][ 'time' ] . ' seconds and ' . $times[ '++$i' ][ 'memory' ] . ' bytes';

ob_end_flush( );

?>

Try it yourself, ;)
up
2
cleong at letstalk dot com
22 years ago
Note that the ++ and -- don't convert a boolean to an int. The following code will loop forever.

function a($start_index) {
for($i = $start_index; $i < 10; $i++) echo "\$i = $i\n";
}

a(false);

This behavior is, of course, very different from that in C. Had me pulling out my hair for a while.
up
-2
Brad Proctor
13 years ago
I ran some tests (on PHP 5.3.3) of my own and was surprised to find $i += 1 to be the fastest method of incrementing.  Here are the methods fastest to slowest:

$i += 1;
++$i;
$i++;
$i = $i + 1;
up
-4
ayyappan dot ashok at gmail dot com
8 years ago
Rule Incrementing or decrementing booleans has no effect.

It has an effort on Incrementing or decrementing booleans.

Please look over the code.

$var = true;
echo ++$var;   //Results 1

Similarly

$var = true;
echo ++$var;   //Results 1

$var = (int)false;
echo ++$var;   //Results 1

$var = (int)false;
echo $var++;   //Results 0;   

Note : Tested on PHP Version 5.5.32
up
-9
sneskid at hotmail dot com
14 years ago
(related to what "Are Pedersen" wrote)
With arrays it can lead to much confusion if your index variable is altered on the right side of the = sign, either with ++|-- or even when passed to a function by reference..
Consider these (PHP 5):
<?php
$A
[$a] = ++$a; // [1]=1
$B[++$b] = ++$b; // [1]=2
$C[$c+=0] = ++$c; // [0]=1
?>
In 'A' you have to be aware that PHP evaluates $A[$a] last.
Yet in 'B' and 'C' PHP evaluates the index and saves it in a temporary variable.

You can always force PHP to evaluate a variable without explicitly storing it as a named variable first, with a simple "+=0" like in example 'C'.

Compared to 'A', 'C' gives the more logically expected result, when we expect evaluation occurs left to right.
PHP does evaluate left to right BUT it will attempt to cut down on temporary variables, which can lead to confusing results.

So just be aware and use either behavior to your advantage for the desired functionality.
up
-12
fred at surleau dot com
22 years ago
Other samples :
$l="A";      $l++; -> $l="B"
$l="A0";     $l++; -> $l="A1"
$l="A9";     $l++; -> $l="B0"
$l="Z99";    $l++; -> $l="AA00"
$l="5Z9";    $l++; -> $l="6A0"
$l="9Z9";    $l++; -> $l="10A0"
$l="9z9";    $l++; -> $l="10a0"
$l="J85410"; $l++; -> $l="J85411"
$l="J99999"; $l++; -> $l="K00000"
$l="K00000"; $l++; -> $l="K00001"
up
-4
leo zandvliet
5 years ago
Please note the difference between post-incrementing in a for-loop and recursive function calls (don't use it in the latter!).

<?php
$increment
= $preIncrement = $postIncrement = 1;
echo
$increment.' - '.$preIncrement.' - '.$postIncrement;
echo
'<br>';
echo (
$increment+1).' - '.(++$preIncrement).' - '.($postIncrement++);
echo
'<br>';
echo (
$increment+1).' - '.(++$preIncrement).' - '.($postIncrement++);
echo
'<br>';
echo (
$increment+1).' - '.(++$preIncrement).' - '.($postIncrement++);
?>

Outputs:
1 - 1 - 1
2 - 2 - 1
2 - 3 - 2
2 - 4 - 3

The for-loop:
<?php
for($i=0; $i<4; $i++)
{
    echo
$i.'<br>';
}
?>

Outputs:
0
1
2
3

And the 'headache' mistake, post-increment as parameter of a recursive call:
<?php
testFunctionNesting
(3, 1, 1, 1);

function
testFunctionNesting($max, $increment, $preIncrement, $postIncrement)
{   
    echo
$increment.' - '.$preIncrement.' - '.$postIncrement;
    echo
'<br>';
   
    if(
$increment>=$max)
    {
       
$inc = $increment;
       
$pre = $preIncrement;
       
$post = $postIncrement;
        return;
    }
       
   
   
testFunctionNesting($max, ($increment+1), (++$preIncrement), ($postIncrement++));
}
?>

Output shows that the postIncremented value is never really available as incremented value:
1 - 1 - 1
2 - 2 - 1
3 - 3 - 1
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