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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>if</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.control-structures.html">Control Structures</a></div> <div class="next" style="text-align: right; float: right;"><a href="control-structures.else.html">else</a></div> <div class="up"><a href="language.control-structures.html">Control Structures</a></div> <div class="home"><a href="index.html">PHP Manual</a></div></div><hr /><div id="control-structures.if" class="sect1"> <h2 class="title"><i>if</i></h2> <p class="para"> The <i>if</i> construct is one of the most important features of many languages, PHP included. It allows for conditional execution of code fragments. PHP features an <i>if</i> structure that is similar to that of C: <div class="informalexample"> <div class="example-contents"><div class="cdata"><pre>if (expr) statement</pre></div> </div> </div> </p> <p class="simpara"> As described in <a href="language.expressions.html" class="link">the section about expressions</a>, <span class="replaceable">expression</span> is evaluated to its Boolean value. If <span class="replaceable">expression</span> evaluates to <b><tt>TRUE</tt></b>, PHP will execute <span class="replaceable">statement</span>, and if it evaluates to <b><tt>FALSE</tt></b> - it'll ignore it. More information about what values evaluate to <b><tt>FALSE</tt></b> can be found in the <a href="language.types.boolean.html#language.types.boolean.casting" class="link">'Converting to boolean'</a> section. </p> <p class="para"> The following example would display <span class="computeroutput">a is bigger than b</span> if <var class="varname">$a</var> is bigger than <var class="varname">$b</var>: <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">if (</span><span style="color: #0000BB">$a </span><span style="color: #007700">> </span><span style="color: #0000BB">$b</span><span style="color: #007700">)<br /> echo </span><span style="color: #DD0000">"a is bigger than b"</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">?></span></span></code></div> </div> </div> </p> <p class="para"> Often you'd want to have more than one statement to be executed conditionally. Of course, there's no need to wrap each statement with an <i>if</i> clause. Instead, you can group several statements into a statement group. For example, this code would display <span class="computeroutput">a is bigger than b</span> if <var class="varname">$a</var> is bigger than <var class="varname">$b</var>, and would then assign the value of <var class="varname">$a</var> into <var class="varname">$b</var>: <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">if (</span><span style="color: #0000BB">$a </span><span style="color: #007700">> </span><span style="color: #0000BB">$b</span><span style="color: #007700">) {<br /> echo </span><span style="color: #DD0000">"a is bigger than b"</span><span style="color: #007700">;<br /> </span><span style="color: #0000BB">$b </span><span style="color: #007700">= </span><span style="color: #0000BB">$a</span><span style="color: #007700">;<br />}<br /></span><span style="color: #0000BB">?></span></span></code></div> </div> </div> </p> <p class="simpara"> <i>If</i> statements can be nested infinitely within other <i>if</i> statements, which provides you with complete flexibility for conditional execution of the various parts of your program. </p> </div><hr /><div style="text-align: center;"> <div class="prev" style="text-align: left; float: left;"><a href="language.control-structures.html">Control Structures</a></div> <div class="next" style="text-align: right; float: right;"><a href="control-structures.else.html">else</a></div> <div class="up"><a href="language.control-structures.html">Control Structures</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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