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<HTML
><HEAD
><TITLE
>switch</TITLE
><META
NAME="GENERATOR"
CONTENT="Modular DocBook HTML Stylesheet Version 1.57"><LINK
REL="HOME"
TITLE="PHP Manual"
HREF="manual.html"><LINK
REL="UP"
TITLE="Control Structures"
HREF="control-structures.html"><LINK
REL="PREVIOUS"
TITLE="continue"
HREF="control-structures.continue.html"><LINK
REL="NEXT"
TITLE="require"
HREF="function.require.html"><META
NAME="HTTP_EQUIV"
CONTENT="text/html; charset=ISO-8859-1"></HEAD
><BODY
CLASS="sect1"
BGCOLOR="#FFFFFF"
TEXT="#000000"
LINK="#0000FF"
VLINK="#840084"
ALINK="#0000FF"
><DIV
CLASS="NAVHEADER"
><TABLE
WIDTH="100%"
BORDER="0"
CELLPADDING="0"
CELLSPACING="0"
><TR
><TH
COLSPAN="3"
ALIGN="center"
>PHP Manual</TH
></TR
><TR
><TD
WIDTH="10%"
ALIGN="left"
VALIGN="bottom"
><A
HREF="control-structures.continue.html"
>Prev</A
></TD
><TD
WIDTH="80%"
ALIGN="center"
VALIGN="bottom"
>Chapter 11. Control Structures</TD
><TD
WIDTH="10%"
ALIGN="right"
VALIGN="bottom"
><A
HREF="function.require.html"
>Next</A
></TD
></TR
></TABLE
><HR
ALIGN="LEFT"
WIDTH="100%"></DIV
><DIV
CLASS="sect1"
><H1
CLASS="sect1"
><A
NAME="control-structures.switch"
><TT
CLASS="literal"
>switch</TT
></A
></H1
><P
> The <TT
CLASS="literal"
>switch</TT
> statement is similar to a series of
IF statements on the same expression. In many occasions, you may
want to compare the same variable (or expression) with many
different values, and execute a different piece of code depending
on which value it equals to. This is exactly what the
<TT
CLASS="literal"
>switch</TT
> statement is for.
</P
><P
> The following two examples are two different ways to write the
same thing, one using a series of <TT
CLASS="literal"
>if</TT
>
statements, and the other using the <TT
CLASS="literal"
>switch</TT
>
statement:
<DIV
CLASS="informalexample"
><A
NAME="AEN3547"
></A
><P
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="programlisting"
> if ($i == 0) {
print "i equals 0";
}
if ($i == 1) {
print "i equals 1";
}
if ($i == 2) {
print "i equals 2";
}
switch ($i) {
case 0:
print "i equals 0";
break;
case 1:
print "i equals 1";
break;
case 2:
print "i equals 2";
break;
}
</PRE
></TD
></TR
></TABLE
><P
></P
></DIV
>
</P
><P
> It is important to understand how the <TT
CLASS="literal"
>switch</TT
>
statement is executed in order to avoid mistakes. The
<TT
CLASS="literal"
>switch</TT
> statement executes line by line
(actually, statement by statement). In the beginning, no code is
executed. Only when a <TT
CLASS="literal"
>case</TT
> statement is found
with a value that matches the value of the
<TT
CLASS="literal"
>switch</TT
> expression does PHP begin to execute the
statements. PHP continues to execute the statements until the end
of the <TT
CLASS="literal"
>switch</TT
> block, or the first time it sees
a <TT
CLASS="literal"
>break</TT
> statement. If you don't write a
<TT
CLASS="literal"
>break</TT
> statement at the end of a case's
statement list, PHP will go on executing the statements of the
following case. For example:
<DIV
CLASS="informalexample"
><A
NAME="AEN3557"
></A
><P
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="programlisting"
> switch ($i) {
case 0:
print "i equals 0";
case 1:
print "i equals 1";
case 2:
print "i equals 2";
}
</PRE
></TD
></TR
></TABLE
><P
></P
></DIV
>
</P
><P
> Here, if $i equals to 0, PHP would execute all of the print
statements! If $i equals to 1, PHP would execute the last two
print statements, and only if $i equals to 2, you'd get the
'expected' behavior and only 'i equals 2' would be displayed. So,
it's important not to forget <TT
CLASS="literal"
>break</TT
> statements
(even though you may want to avoid supplying them on purpose under
certain circumstances).
</P
><P
> In a <TT
CLASS="literal"
>switch</TT
> statement, the condition is
evaluated only once and the result is compared to each
<TT
CLASS="literal"
>case</TT
> statement. In an <TT
CLASS="literal"
>elseif</TT
>
statement, the condition is evaluated again. If your condition is
more complicated than a simple compare and/or is in a tight loop,
a <TT
CLASS="literal"
>switch</TT
> may be faster.
</P
><P
> The statement list for a case can also be empty, which simply
passes control into the statement list for the next case.
<DIV
CLASS="informalexample"
><A
NAME="AEN3567"
></A
><P
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="programlisting"
> switch ($i) {
case 0:
case 1:
case 2:
print "i is less than 3 but not negative";
break;
case 3:
print "i is 3";
}
</PRE
></TD
></TR
></TABLE
><P
></P
></DIV
>
</P
><P
> A special case is the default case. This case matches anything
that wasn't matched by the other cases. For example:
<DIV
CLASS="informalexample"
><A
NAME="AEN3570"
></A
><P
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="programlisting"
> switch ($i) {
case 0:
print "i equals 0";
break;
case 1:
print "i equals 1";
break;
case 2:
print "i equals 2";
break;
default:
print "i is not equal to 0, 1 or 2";
}
</PRE
></TD
></TR
></TABLE
><P
></P
></DIV
>
</P
><P
> The <TT
CLASS="literal"
>case</TT
> expression may be any expression that
evaluates to a simple type, that is, integer or floating-point
numbers and strings. Arrays or objects cannot be used here unless
they are dereferenced to a simple type.
</P
><P
> The alternative syntax for control structures is supported with
switches. For more information, see <A
HREF="control-structures.alternative-syntax.html"
>Alternative syntax
for control structures</A
> .
<DIV
CLASS="informalexample"
><A
NAME="AEN3576"
></A
><P
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="programlisting"
> switch ($i):
case 0:
print "i equals 0";
break;
case 1:
print "i equals 1";
break;
case 2:
print "i equals 2";
break;
default:
print "i is not equal to 0, 1 or 2";
endswitch;
</PRE
></TD
></TR
></TABLE
><P
></P
></DIV
>
</P
></DIV
><DIV
CLASS="NAVFOOTER"
><HR
ALIGN="LEFT"
WIDTH="100%"><TABLE
WIDTH="100%"
BORDER="0"
CELLPADDING="0"
CELLSPACING="0"
><TR
><TD
WIDTH="33%"
ALIGN="left"
VALIGN="top"
><A
HREF="control-structures.continue.html"
>Prev</A
></TD
><TD
WIDTH="34%"
ALIGN="center"
VALIGN="top"
><A
HREF="manual.html"
>Home</A
></TD
><TD
WIDTH="33%"
ALIGN="right"
VALIGN="top"
><A
HREF="function.require.html"
>Next</A
></TD
></TR
><TR
><TD
WIDTH="33%"
ALIGN="left"
VALIGN="top"
><TT
CLASS="literal"
>continue</TT
></TD
><TD
WIDTH="34%"
ALIGN="center"
VALIGN="top"
><A
HREF="control-structures.html"
>Up</A
></TD
><TD
WIDTH="33%"
ALIGN="right"
VALIGN="top"
><A
HREF="function.require.html"
><B
CLASS="function"
>require()</B
></A
></TD
></TR
></TABLE
></DIV
></BODY
></HTML
>