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.

Table 15-6. Increment/decrement Operators

ExampleNameEffect
++$aPre-incrementIncrements $a by one, then returns $a.
$a++Post-incrementReturns $a, then increments $a by one.
--$aPre-decrementDecrements $a by one, then returns $a.
$a--Post-decrementReturns $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 15-4. 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.

© Copyright 2003-2014 www.php-editors.com. The ultimate PHP Editor and PHP IDE site.