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<title>Incrementing/Decrementing Operators</title>
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</div><hr /><div id="language.operators.increment" class="sect1">
<h2 class="title">Incrementing/Decrementing Operators</h2>
<p class="para">
PHP supports C-style pre- and post-increment and decrement
operators.
</p>
<blockquote class="note"><p><strong class="note">Note</strong>:
<span class="simpara">
The increment/decrement operators only affect numbers and strings.
Arrays, objects and resources are not affected.
Decrementing <strong><code>NULL</code></strong> values has no effect too, but incrementing them
results in <em>1</em>.
</span>
</p></blockquote>
<table class="doctable table">
<caption><strong>Increment/decrement Operators</strong></caption>
<thead>
<tr>
<th>Example</th>
<th>Name</th>
<th>Effect</th>
</tr>
</thead>
<tbody class="tbody">
<tr>
<td>++$a</td>
<td>Pre-increment</td>
<td>Increments <var class="varname"><var class="varname">$a</var></var> by one, then returns <var class="varname"><var class="varname">$a</var></var>.</td>
</tr>
<tr>
<td>$a++</td>
<td>Post-increment</td>
<td>Returns <var class="varname"><var class="varname">$a</var></var>, then increments <var class="varname"><var class="varname">$a</var></var> by one.</td>
</tr>
<tr>
<td>--$a</td>
<td>Pre-decrement</td>
<td>Decrements <var class="varname"><var class="varname">$a</var></var> by one, then returns <var class="varname"><var class="varname">$a</var></var>.</td>
</tr>
<tr>
<td>$a--</td>
<td>Post-decrement</td>
<td>Returns <var class="varname"><var class="varname">$a</var></var>, then decrements <var class="varname"><var class="varname">$a</var></var> by one.</td>
</tr>
</tbody>
</table>
<p class="para">
Here's a simple example script:
<div class="informalexample">
<div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br /></span><span style="color: #007700">echo </span><span style="color: #DD0000">"<h3>Postincrement</h3>"</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">$a </span><span style="color: #007700">= </span><span style="color: #0000BB">5</span><span style="color: #007700">;<br />echo </span><span style="color: #DD0000">"Should be 5: " </span><span style="color: #007700">. </span><span style="color: #0000BB">$a</span><span style="color: #007700">++ . </span><span style="color: #DD0000">"<br />\n"</span><span style="color: #007700">;<br />echo </span><span style="color: #DD0000">"Should be 6: " </span><span style="color: #007700">. </span><span style="color: #0000BB">$a </span><span style="color: #007700">. </span><span style="color: #DD0000">"<br />\n"</span><span style="color: #007700">;<br /><br />echo </span><span style="color: #DD0000">"<h3>Preincrement</h3>"</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">$a </span><span style="color: #007700">= </span><span style="color: #0000BB">5</span><span style="color: #007700">;<br />echo </span><span style="color: #DD0000">"Should be 6: " </span><span style="color: #007700">. ++</span><span style="color: #0000BB">$a </span><span style="color: #007700">. </span><span style="color: #DD0000">"<br />\n"</span><span style="color: #007700">;<br />echo </span><span style="color: #DD0000">"Should be 6: " </span><span style="color: #007700">. </span><span style="color: #0000BB">$a </span><span style="color: #007700">. </span><span style="color: #DD0000">"<br />\n"</span><span style="color: #007700">;<br /><br />echo </span><span style="color: #DD0000">"<h3>Postdecrement</h3>"</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">$a </span><span style="color: #007700">= </span><span style="color: #0000BB">5</span><span style="color: #007700">;<br />echo </span><span style="color: #DD0000">"Should be 5: " </span><span style="color: #007700">. </span><span style="color: #0000BB">$a</span><span style="color: #007700">-- . </span><span style="color: #DD0000">"<br />\n"</span><span style="color: #007700">;<br />echo </span><span style="color: #DD0000">"Should be 4: " </span><span style="color: #007700">. </span><span style="color: #0000BB">$a </span><span style="color: #007700">. </span><span style="color: #DD0000">"<br />\n"</span><span style="color: #007700">;<br /><br />echo </span><span style="color: #DD0000">"<h3>Predecrement</h3>"</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">$a </span><span style="color: #007700">= </span><span style="color: #0000BB">5</span><span style="color: #007700">;<br />echo </span><span style="color: #DD0000">"Should be 4: " </span><span style="color: #007700">. --</span><span style="color: #0000BB">$a </span><span style="color: #007700">. </span><span style="color: #DD0000">"<br />\n"</span><span style="color: #007700">;<br />echo </span><span style="color: #DD0000">"Should be 4: " </span><span style="color: #007700">. </span><span style="color: #0000BB">$a </span><span style="color: #007700">. </span><span style="color: #DD0000">"<br />\n"</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
</div>
</p>
<p class="para">
PHP follows Perl's convention when dealing with arithmetic operations
on character variables and not C's. For example, in PHP and Perl
<em>$a = 'Z'; $a++;</em> turns <em>$a</em> into <em>'AA'</em>, while in C
<em>a = 'Z'; a++;</em> turns <em>a</em> into <em>'['</em>
(ASCII value of <em>'Z'</em> is 90, ASCII value of <em>'['</em> 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.
<div class="example" id="example-125">
<p><strong>Example #1 Arithmetic Operations on Character Variables</strong></p>
<div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br /></span><span style="color: #007700">echo </span><span style="color: #DD0000">'== Alphabets ==' </span><span style="color: #007700">. </span><span style="color: #0000BB">PHP_EOL</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">$s </span><span style="color: #007700">= </span><span style="color: #DD0000">'W'</span><span style="color: #007700">;<br />for (</span><span style="color: #0000BB">$n</span><span style="color: #007700">=</span><span style="color: #0000BB">0</span><span style="color: #007700">; </span><span style="color: #0000BB">$n</span><span style="color: #007700"><</span><span style="color: #0000BB">6</span><span style="color: #007700">; </span><span style="color: #0000BB">$n</span><span style="color: #007700">++) {<br /> echo ++</span><span style="color: #0000BB">$s </span><span style="color: #007700">. </span><span style="color: #0000BB">PHP_EOL</span><span style="color: #007700">;<br />}<br /></span><span style="color: #FF8000">// Digit characters behave differently<br /></span><span style="color: #007700">echo </span><span style="color: #DD0000">'== Digits ==' </span><span style="color: #007700">. </span><span style="color: #0000BB">PHP_EOL</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">$d </span><span style="color: #007700">= </span><span style="color: #DD0000">'A8'</span><span style="color: #007700">;<br />for (</span><span style="color: #0000BB">$n</span><span style="color: #007700">=</span><span style="color: #0000BB">0</span><span style="color: #007700">; </span><span style="color: #0000BB">$n</span><span style="color: #007700"><</span><span style="color: #0000BB">6</span><span style="color: #007700">; </span><span style="color: #0000BB">$n</span><span style="color: #007700">++) {<br /> echo ++</span><span style="color: #0000BB">$d </span><span style="color: #007700">. </span><span style="color: #0000BB">PHP_EOL</span><span style="color: #007700">;<br />}<br /></span><span style="color: #0000BB">$d </span><span style="color: #007700">= </span><span style="color: #DD0000">'A08'</span><span style="color: #007700">;<br />for (</span><span style="color: #0000BB">$n</span><span style="color: #007700">=</span><span style="color: #0000BB">0</span><span style="color: #007700">; </span><span style="color: #0000BB">$n</span><span style="color: #007700"><</span><span style="color: #0000BB">6</span><span style="color: #007700">; </span><span style="color: #0000BB">$n</span><span style="color: #007700">++) {<br /> echo ++</span><span style="color: #0000BB">$d </span><span style="color: #007700">. </span><span style="color: #0000BB">PHP_EOL</span><span style="color: #007700">;<br />}<br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
<div class="example-contents"><p>The above example will output:</p></div>
<div class="example-contents screen">
<div class="cdata"><pre>
== Characters ==
X
Y
Z
AA
AB
AC
== Digits ==
A9
B0
B1
B2
B3
B4
A09
A10
A11
A12
A13
A14
</pre></div>
</div>
</div>
</p>
<p class="para">
Incrementing or decrementing booleans has no effect.
</p>
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