php increment/decrement operator

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

Note: Increment/decrement operators do not affect Boolean values. Decrementing a NULL value has no effect, but increasing NULL results in 1.

Increment/Decrease Operator

Example

Name

Effect

++$a Prepend the value of $a by one, and then return $a.

$a++ followed by , returns $a, and then adds one to the value of $a.

--$a Subtracts the value of $a by one, and then returns $a.

$a-- After subtraction returns $a, and then decrements the value of $a by one.

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";
?>

When dealing with arithmetic operations on character variables, PHP follows Perl's habits instead of C's. For example, in Perl $a = 'Z'; $a++; will turn $a into 'AA', while in C, a = 'Z'; a++; will turn a into '['('Z' The ASCII value of '[' is 90, and the ASCII value of '[' is 91). Note that character variables can only be incremented, not decremented, and only pure letters (a-z and A-Z) are supported. Incrementing/decrementing other character variables is invalid and the original string will not change.

Example #1 Arithmetic operations involving character variables

<?php
$i = &#39;W&#39;;
for ($n=0; $n<6; $n++) {
    echo ++$i . "\n";
}
?>

The above routine will output:

X
Y
Z
AA
AB
AC