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Source of: /manual/en/language.operators.increment.php

<?php
include_once $_SERVER['DOCUMENT_ROOT'] . '/include/shared-manual.inc';
$TOC = array();
$PARENTS = array();
include_once dirname(__FILE__) ."/toc/language.operators.inc";
$setup = array (
  'home' =>
  array (
    0 => 'index.php',
    1 => 'PHP Manual',
  ),
  'head' =>
  array (
    0 => 'UTF-8',
    1 => 'en',
  ),
  'this' =>
  array (
    0 => 'language.operators.increment.php',
    1 => 'Incrementing/Decrementing Operators',
  ),
  'up' =>
  array (
    0 => 'language.operators.php',
    1 => 'Operators',
  ),
  'prev' =>
  array (
    0 => 'language.operators.execution.php',
    1 => 'Execution Operators',
  ),
  'next' =>
  array (
    0 => 'language.operators.logical.php',
    1 => 'Logical Operators',
  ),
);
$setup["toc"] = $TOC;
$setup["parents"] = $PARENTS;
manual_setup($setup);

manual_header();
?>
<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><p><b class="note">Note</b>:
    <span class="simpara">
     The increment/decrement operators do not affect boolean values.
     Decrementing <b><tt class="constant">NULL</tt></b> values has no effect too, but incrementing them
     results in <i>1</i>.
    </span>
   </p></blockquote>
   <table class="doctable table">
    <caption><b>Increment/decrement Operators</b></caption>
   
     <thead valign="middle">
      <tr valign="middle">
       <th>Example</th>
       <th>Name</th>
       <th>Effect</th>
      </tr>

     </thead>

     <tbody valign="middle" class="tbody">
      <tr valign="middle">
       <td align="left">++$a</td>
       <td align="left">Pre-increment</td>
       <td align="left">Increments <var class="varname">$a</var> by one, then returns <var class="varname">$a</var>.</td>
      </tr>

      <tr valign="middle">
       <td align="left">$a++</td>
       <td align="left">Post-increment</td>
       <td align="left">Returns <var class="varname">$a</var>, then increments <var class="varname">$a</var> by one.</td>
      </tr>

      <tr valign="middle">
       <td align="left">--$a</td>
       <td align="left">Pre-decrement</td>
       <td align="left">Decrements <var class="varname">$a</var> by one, then returns <var class="varname">$a</var>.</td>
      </tr>

      <tr valign="middle">
       <td align="left">$a--</td>
       <td align="left">Post-decrement</td>
       <td align="left">Returns <var class="varname">$a</var>, then decrements <var class="varname">$a</var> by one.</td>
      </tr>

     </tbody>
   
   </table>

   <p class="para">
    Here&#039;s a simple example script:
    </p><div class="informalexample">
     <div class="example-contents programlisting">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB">&lt;?php<br /></span><span style="color: #007700">echo&nbsp;</span><span style="color: #DD0000">"&lt;h3&gt;Postincrement&lt;/h3&gt;"</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">$a&nbsp;</span><span style="color: #007700">=&nbsp;</span><span style="color: #0000BB">5</span><span style="color: #007700">;<br />echo&nbsp;</span><span style="color: #DD0000">"Should&nbsp;be&nbsp;5:&nbsp;"&nbsp;</span><span style="color: #007700">.&nbsp;</span><span style="color: #0000BB">$a</span><span style="color: #007700">++&nbsp;.&nbsp;</span><span style="color: #DD0000">"&lt;br&nbsp;/&gt;\n"</span><span style="color: #007700">;<br />echo&nbsp;</span><span style="color: #DD0000">"Should&nbsp;be&nbsp;6:&nbsp;"&nbsp;</span><span style="color: #007700">.&nbsp;</span><span style="color: #0000BB">$a&nbsp;</span><span style="color: #007700">.&nbsp;</span><span style="color: #DD0000">"&lt;br&nbsp;/&gt;\n"</span><span style="color: #007700">;<br /><br />echo&nbsp;</span><span style="color: #DD0000">"&lt;h3&gt;Preincrement&lt;/h3&gt;"</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">$a&nbsp;</span><span style="color: #007700">=&nbsp;</span><span style="color: #0000BB">5</span><span style="color: #007700">;<br />echo&nbsp;</span><span style="color: #DD0000">"Should&nbsp;be&nbsp;6:&nbsp;"&nbsp;</span><span style="color: #007700">.&nbsp;++</span><span style="color: #0000BB">$a&nbsp;</span><span style="color: #007700">.&nbsp;</span><span style="color: #DD0000">"&lt;br&nbsp;/&gt;\n"</span><span style="color: #007700">;<br />echo&nbsp;</span><span style="color: #DD0000">"Should&nbsp;be&nbsp;6:&nbsp;"&nbsp;</span><span style="color: #007700">.&nbsp;</span><span style="color: #0000BB">$a&nbsp;</span><span style="color: #007700">.&nbsp;</span><span style="color: #DD0000">"&lt;br&nbsp;/&gt;\n"</span><span style="color: #007700">;<br /><br />echo&nbsp;</span><span style="color: #DD0000">"&lt;h3&gt;Postdecrement&lt;/h3&gt;"</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">$a&nbsp;</span><span style="color: #007700">=&nbsp;</span><span style="color: #0000BB">5</span><span style="color: #007700">;<br />echo&nbsp;</span><span style="color: #DD0000">"Should&nbsp;be&nbsp;5:&nbsp;"&nbsp;</span><span style="color: #007700">.&nbsp;</span><span style="color: #0000BB">$a</span><span style="color: #007700">--&nbsp;.&nbsp;</span><span style="color: #DD0000">"&lt;br&nbsp;/&gt;\n"</span><span style="color: #007700">;<br />echo&nbsp;</span><span style="color: #DD0000">"Should&nbsp;be&nbsp;4:&nbsp;"&nbsp;</span><span style="color: #007700">.&nbsp;</span><span style="color: #0000BB">$a&nbsp;</span><span style="color: #007700">.&nbsp;</span><span style="color: #DD0000">"&lt;br&nbsp;/&gt;\n"</span><span style="color: #007700">;<br /><br />echo&nbsp;</span><span style="color: #DD0000">"&lt;h3&gt;Predecrement&lt;/h3&gt;"</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">$a&nbsp;</span><span style="color: #007700">=&nbsp;</span><span style="color: #0000BB">5</span><span style="color: #007700">;<br />echo&nbsp;</span><span style="color: #DD0000">"Should&nbsp;be&nbsp;4:&nbsp;"&nbsp;</span><span style="color: #007700">.&nbsp;--</span><span style="color: #0000BB">$a&nbsp;</span><span style="color: #007700">.&nbsp;</span><span style="color: #DD0000">"&lt;br&nbsp;/&gt;\n"</span><span style="color: #007700">;<br />echo&nbsp;</span><span style="color: #DD0000">"Should&nbsp;be&nbsp;4:&nbsp;"&nbsp;</span><span style="color: #007700">.&nbsp;</span><span style="color: #0000BB">$a&nbsp;</span><span style="color: #007700">.&nbsp;</span><span style="color: #DD0000">"&lt;br&nbsp;/&gt;\n"</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">?&gt;</span>
</span>
</code></div>
     </div>

    </div><p>
   </p>
   <p class="para">
    PHP follows Perl&#039;s convention when dealing with arithmetic operations
    on character variables and not C&#039;s.  For example, in Perl
    <i>&#039;Z&#039;+1</i> turns into <i>&#039;AA&#039;</i>, while in C
    <i>&#039;Z&#039;+1</i> turns into <i>&#039;[&#039;</i>
    ( <i>ord(&#039;Z&#039;) == 90</i>, <i>ord(&#039;[&#039;) == 91</i> ).
    Note that character variables can be incremented but not decremented and
    even so only plain ASCII characters (a-z and A-Z) are supported.
    </p><div class="example">
     <p><b>Example #1 Arithmetic Operations on Character Variables</b></p>
     <div class="example-contents programlisting">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB">&lt;?php<br />$i&nbsp;</span><span style="color: #007700">=&nbsp;</span><span style="color: #DD0000">'W'</span><span style="color: #007700">;<br />for&nbsp;(</span><span style="color: #0000BB">$n</span><span style="color: #007700">=</span><span style="color: #0000BB">0</span><span style="color: #007700">;&nbsp;</span><span style="color: #0000BB">$n</span><span style="color: #007700">&lt;</span><span style="color: #0000BB">6</span><span style="color: #007700">;&nbsp;</span><span style="color: #0000BB">$n</span><span style="color: #007700">++)&nbsp;{<br />&nbsp;&nbsp;&nbsp;&nbsp;echo&nbsp;++</span><span style="color: #0000BB">$i&nbsp;</span><span style="color: #007700">.&nbsp;</span><span style="color: #DD0000">"\n"</span><span style="color: #007700">;<br />}<br /></span><span style="color: #0000BB">?&gt;</span>
</span>
</code></div>
     </div>

     <div class="example-contents para"><p>The above example will output:</p></div>
     <div class="example-contents screen">
<div class="cdata"><pre>
X
Y
Z
AA
AB
AC
</pre></div>
     </div>
    </div><p>
   </p>
   <p class="para">
    Incrementing or decrementing booleans has no effect.
   </p>
  </div><?php manual_footer(); ?>
 
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