Source of: /manual/en/control-structures.if.php
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<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:
</p><div class="informalexample">
<div class="example-contents programlisting">
<div class="cdata"><pre>
if (expr)
statement
</pre></div>
</div>
</div><p>
</p>
<p class="simpara">
As described in <a href="language.expressions.php" 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 class="constant">TRUE</tt></b>,
PHP will execute <span class="replaceable">statement</span>, and if it evaluates
to <b><tt class="constant">FALSE</tt></b> - it'll ignore it. More information about what values evaluate
to <b><tt class="constant">FALSE</tt></b> can be found in the <a href="language.types.boolean.php#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>:
</p><div class="informalexample">
<div class="example-contents programlisting">
<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>
<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>:
</p><div class="informalexample">
<div class="example-contents programlisting">
<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>
<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><?php manual_footer(); ?>
