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PHP Manual


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 PHP and Perl $a = 'Z'; $a++; turns $a into 'AA', while in C a = 'Z'; a++; turns a into '[' (ASCII value of 'Z' is 90, ASCII value of '[' is 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. Incrementing/decrementing other character variables has no effect, the original string is unchanged.

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.




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