Incrementing/Decrementing Operators

Error Control Operators
November 13, 2018
Logical Operators
November 13, 2018
Incrementing/Decrementing Operators

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

NoteThe increment/decrement operators only affect numbers and strings. Arrays, objects and resources are not affected. 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:

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 alphabets and digits (a-z, A-Z and 0-9) are supported. Incrementing/decrementing other character variables has no effect, the original string is unchanged.

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Sondiva Technologies
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