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<HTML
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><TITLE
>Control Structures</TITLE
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><DIV
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><H1
><A
NAME="control-structures"
>Chapter 11. Control Structures</A
></H1
><DIV
CLASS="TOC"
><DL
><DT
><B
>Table of Contents</B
></DT
><DT
><A
HREF="control-structures.html#control-structures.if"
><TT
CLASS="literal"
>if</TT
></A
></DT
><DT
><A
HREF="control-structures.else.html"
><TT
CLASS="literal"
>else</TT
></A
></DT
><DT
><A
HREF="control-structures.elseif.html"
><TT
CLASS="literal"
>elseif</TT
></A
></DT
><DT
><A
HREF="control-structures.alternative-syntax.html"
>Alternative syntax for control structures</A
></DT
><DT
><A
HREF="control-structures.while.html"
><TT
CLASS="literal"
>while</TT
></A
></DT
><DT
><A
HREF="control-structures.do.while.html"
><TT
CLASS="literal"
>do..while</TT
></A
></DT
><DT
><A
HREF="control-structures.for.html"
><TT
CLASS="literal"
>for</TT
></A
></DT
><DT
><A
HREF="control-structures.foreach.html"
><TT
CLASS="literal"
>foreach</TT
></A
></DT
><DT
><A
HREF="control-structures.break.html"
><TT
CLASS="literal"
>break</TT
></A
></DT
><DT
><A
HREF="control-structures.continue.html"
><TT
CLASS="literal"
>continue</TT
></A
></DT
><DT
><A
HREF="control-structures.switch.html"
><TT
CLASS="literal"
>switch</TT
></A
></DT
><DT
><A
HREF="function.require.html"
><A
HREF="function.require.html"
><B
CLASS="function"
>require()</B
></A
></A
></DT
><DT
><A
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><A
HREF="function.include.html"
><B
CLASS="function"
>include()</B
></A
></A
></DT
><DT
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><A
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><B
CLASS="function"
>require_once()</B
></A
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><B
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>include_once()</B
></A
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><P
>&#13;   Any PHP script is built out of a series of statements. A statement
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   statement of even a statement that does nothing (an empty
   statement). Statements usually end with a semicolon. In addition,
   statements can be grouped into a statement-group by encapsulating a
   group of statements with curly braces. A statement-group is a
   statement by itself as well. The various statement types are
   described in this chapter.
  </P
><DIV
CLASS="sect1"
><H1
CLASS="sect1"
><A
NAME="control-structures.if"
><TT
CLASS="literal"
>if</TT
></A
></H1
><P
>&#13;    The <TT
CLASS="literal"
>if</TT
> construct is one of the most important
    features of many languages, PHP included.  It allows for
    conditional execution of code fragments.  PHP features an
    <TT
CLASS="literal"
>if</TT
> structure that is similar to that of C:
    <DIV
CLASS="informalexample"
><A
NAME="AEN3298"
></A
><P
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="programlisting"
>&#13;if (expr)
    statement
     </PRE
></TD
></TR
></TABLE
><P
></P
></DIV
>
   </P
><P
>&#13;    As described in the section about expressions, expr is evaluated
    to its truth value.  If <TT
CLASS="replaceable"
><I
>expr</I
></TT
> evaluates
    to <TT
CLASS="literal"
>TRUE</TT
>, PHP will execute statement, and if it
    evaluates to <TT
CLASS="literal"
>FALSE</TT
> - it'll ignore it.
   </P
><P
>&#13;    The following example would display <TT
CLASS="computeroutput"
>a is bigger
    than b</TT
> if <TT
CLASS="replaceable"
><I
>$a</I
></TT
> is bigger
    than <TT
CLASS="replaceable"
><I
>$b</I
></TT
>:
    <DIV
CLASS="informalexample"
><A
NAME="AEN3308"
></A
><P
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="programlisting"
>&#13;if ($a &#62; $b)
    print "a is bigger than b";
     </PRE
></TD
></TR
></TABLE
><P
></P
></DIV
>
   </P
><P
>&#13;    Often you'd want to have more than one statement to be executed
    conditionally.  Of course, there's no need to wrap each statement
    with an <TT
CLASS="literal"
>if</TT
> clause.  Instead, you can group
    several statements into a statement group.  For example, this code
    would display <TT
CLASS="computeroutput"
>a is bigger than b</TT
>
    if <TT
CLASS="replaceable"
><I
>$a</I
></TT
> is bigger than
    <TT
CLASS="replaceable"
><I
>$b</I
></TT
>, and would then assign the value of
    <TT
CLASS="replaceable"
><I
>$a</I
></TT
> into <TT
CLASS="replaceable"
><I
>$b</I
></TT
>:
    <DIV
CLASS="informalexample"
><A
NAME="AEN3317"
></A
><P
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="programlisting"
>&#13;if ($a &#62; $b) {
    print "a is bigger than b";
    $b = $a;
}
     </PRE
></TD
></TR
></TABLE
><P
></P
></DIV
>
   </P
><P
>&#13;    If statements can be nested indefinitely within other
    <TT
CLASS="literal"
>if</TT
> statements, which provides you with complete
    flexibility for conditional execution of the various parts of your
    program.
   </P
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