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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"><html> <head> <title>Incrementing/Decrementing Operators</title> <meta http-equiv="content-type" content="text/html; charset=UTF-8"> </head> <body><div style="text-align: center;"> <div class="prev" style="text-align: left; float: left;"><a href="language.operators.execution.html">Execution Operators</a></div> <div class="next" style="text-align: right; float: right;"><a href="language.operators.logical.html">Logical Operators</a></div> <div class="up"><a href="language.operators.html">Operators</a></div> <div class="home"><a href="index.html">PHP Manual</a></div></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><p><b class="note">Note</b>: <span class="simpara"> The increment/decrement operators do not affect boolean values. Decrementing <b><tt>NULL</tt></b> values has no effect too, but incrementing them results in <i>1</i>. </span> </p></blockquote> <table border="5"> <caption><b>Increment/decrement Operators</b></caption> <colgroup> <thead valign="middle"> <tr valign="middle"> <th colspan="1">Example</th> <th colspan="1">Name</th> <th colspan="1">Effect</th> </tr> </thead> <tbody valign="middle" class="tbody"> <tr valign="middle"> <td colspan="1" rowspan="1" align="left">++$a</td> <td colspan="1" rowspan="1" align="left">Pre-increment</td> <td colspan="1" rowspan="1" align="left">Increments $a by one, then returns $a.</td> </tr> <tr valign="middle"> <td colspan="1" rowspan="1" align="left">$a++</td> <td colspan="1" rowspan="1" align="left">Post-increment</td> <td colspan="1" rowspan="1" align="left">Returns $a, then increments $a by one.</td> </tr> <tr valign="middle"> <td colspan="1" rowspan="1" align="left">--$a</td> <td colspan="1" rowspan="1" align="left">Pre-decrement</td> <td colspan="1" rowspan="1" align="left">Decrements $a by one, then returns $a.</td> </tr> <tr valign="middle"> <td colspan="1" rowspan="1" align="left">$a--</td> <td colspan="1" rowspan="1" align="left">Post-decrement</td> <td colspan="1" rowspan="1" align="left">Returns $a, then decrements $a by one.</td> </tr> </tbody> </colgroup> </table> <p class="para"> Here's a simple example script: <div class="informalexample"> <div class="example-contents"><div class="phpcode"><code><span style="color: #000000"><span style="color: #0000BB"><?php<br /></span><span style="color: #007700">echo </span><span style="color: #DD0000">"<h3>Postincrement</h3>"</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">$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">$a </span><span style="color: #007700">. </span><span style="color: #DD0000">"<br />\n"</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">?></span></span></code></div> </div> </div> </p> <p class="para"> PHP follows Perl's convention when dealing with arithmetic operations on character variables and not C's. For example, in Perl 'Z'+1 turns into 'AA', while in C 'Z'+1 turns into '[' ( ord('Z') == 90, ord('[') == 91 ). Note that character variables can be incremented but not decremented and even so only plain ASCII characters (a-z and A-Z) are supported. <div class="example"> <p><b>Example #1 Arithmetic Operations on Character Variables</b></p> <div class="example-contents"><div class="phpcode"><code><span style="color: #000000"><span style="color: #0000BB"><?php<br />$i </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">$n</span><span style="color: #007700">++) {<br /> echo ++</span><span style="color: #0000BB">$i </span><span style="color: #007700">. </span><span style="color: #DD0000">"\n"</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"><pre><div class="cdata"><pre>XYZAAABAC</pre></div> </pre></div> </div> </p> <p class="para"> Incrementing or decrementing booleans has no effect. </p> </div><hr /><div style="text-align: center;"> <div class="prev" style="text-align: left; float: left;"><a href="language.operators.execution.html">Execution Operators</a></div> <div class="next" style="text-align: right; float: right;"><a href="language.operators.logical.html">Logical Operators</a></div> <div class="up"><a href="language.operators.html">Operators</a></div> <div class="home"><a href="index.html">PHP Manual</a></div></div></body></html>⌨️ 快捷键说明
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