PHP: Incrementing/Decrementing Operators

Incrementing/Decrementing Operators

PHP supports C-style pre- and post-increment and decrement operators.

Note: The increment/decrement operators do not affect boolean values. Decrementing NULL values has no effect too, but incrementing them results in 1.

**Increment/decrement Operators**
Example	Name	Effect
++$a	Pre-increment	Increments $a by one, then returns $a.
$a++	Post-increment	Returns $a, then increments $a by one.
--$a	Pre-decrement	Decrements $a by one, then returns $a.
$a--	Post-decrement	Returns $a, then decrements $a by one.

Here's a simple example script:


<?php

echo "<h3>Postincrement</h3>";

$a = 5;

echo "Should be 5: " . $a++ . "<br />\n";

echo "Should be 6: " . $a . "<br />\n";



echo "<h3>Preincrement</h3>";

$a = 5;

echo "Should be 6: " . ++$a . "<br />\n";

echo "Should be 6: " . $a . "<br />\n";



echo "<h3>Postdecrement</h3>";

$a = 5;

echo "Should be 5: " . $a-- . "<br />\n";

echo "Should be 4: " . $a . "<br />\n";



echo "<h3>Predecrement</h3>";

$a = 5;

echo "Should be 4: " . --$a . "<br />\n";

echo "Should be 4: " . $a . "<br />\n";

?>

PHP follows Perl's convention when dealing with arithmetic operations on character variables and not C's. For example, in Perl 'Z'+1 turns into 'AA', while in C 'Z'+1 turns into '[' ( ord('Z') == 90, ord('[') == 91 ). Note that character variables can be incremented but not decremented and even so only plain ASCII characters (a-z and A-Z) are supported.

Example #1 Arithmetic Operations on Character Variables


<?php

$i = 'W';

for ($n=0; $n<6; $n++) {

    echo ++$i . "\n";

}

?>

The above example will output:

X
Y
Z
AA
AB
AC

Incrementing or decrementing booleans has no effect.