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><H1
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><A
NAME="control-structures.for"
><TT
CLASS="literal"
>for</TT
></A
></H1
><P
> <TT
CLASS="literal"
>for</TT
> loops are the most complex loops in PHP.
They behave like their C counterparts. The syntax of a
<TT
CLASS="literal"
>for</TT
> loop is:
<DIV
CLASS="informalexample"
><P
></P
><TABLE
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><TR
><TD
><PRE
CLASS="programlisting"
> 1
2 for (expr1; expr2; expr3) statement
3 </PRE
></TD
></TR
></TABLE
><P
></P
></DIV
>
</P
><P
> The first expression (<TT
CLASS="replaceable"
><I
>expr1</I
></TT
>) is
evaluated (executed) once unconditionally at the beginning of the
loop.
</P
><P
> In the beginning of each iteration,
<TT
CLASS="replaceable"
><I
>expr2</I
></TT
> is evaluated. If it evaluates to
<TT
CLASS="literal"
>TRUE</TT
>, the loop continues and the nested
statement(s) are executed. If it evaluates to
<TT
CLASS="literal"
>FALSE</TT
>, the execution of the loop ends.
</P
><P
> At the end of each iteration, <TT
CLASS="replaceable"
><I
>expr3</I
></TT
> is
evaluated (executed).
</P
><P
> Each of the expressions can be empty.
<TT
CLASS="replaceable"
><I
>expr2</I
></TT
> being empty means the loop should
be run indefinitely (PHP implicitly considers it as
<TT
CLASS="literal"
>TRUE</TT
>, like C). This may not be as useless as
you might think, since often you'd want to end the loop using a
conditional <A
HREF="control-structures.break.html"
><TT
CLASS="literal"
>break</TT
></A
>
statement instead of using the <TT
CLASS="literal"
>for</TT
> truth
expression.
</P
><P
> Consider the following examples. All of them display numbers from
1 to 10:
<DIV
CLASS="informalexample"
><P
></P
><TABLE
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><TR
><TD
><PRE
CLASS="programlisting"
> 1
2 /* example 1 */
3
4 for ($i = 1; $i <= 10; $i++) {
5 print $i;
6 }
7
8 /* example 2 */
9
10 for ($i = 1;;$i++) {
11 if ($i > 10) {
12 break;
13 }
14 print $i;
15 }
16
17 /* example 3 */
18
19 $i = 1;
20 for (;;) {
21 if ($i > 10) {
22 break;
23 }
24 print $i;
25 $i++;
26 }
27
28 /* example 4 */
29
30 for ($i = 1; $i <= 10; print $i, $i++) ;
31 </PRE
></TD
></TR
></TABLE
><P
></P
></DIV
>
</P
><P
> Of course, the first example appears to be the nicest one (or
perhaps the fourth), but you may find that being able to use empty
expressions in <TT
CLASS="literal"
>for</TT
> loops comes in handy in many
occasions.
</P
><P
> PHP also supports the alternate "colon syntax" for
<TT
CLASS="literal"
>for</TT
> loops.
<DIV
CLASS="informalexample"
><P
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
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><TR
><TD
><PRE
CLASS="programlisting"
> 1
2 for (expr1; expr2; expr3): statement; ...; endfor;
3 </PRE
></TD
></TR
></TABLE
><P
></P
></DIV
>
</P
><P
> Other languages have a <TT
CLASS="literal"
>foreach</TT
> statement to
traverse an array or hash. PHP3 has no such construct; PHP4 does
(see <A
HREF="control-structures.foreach.html"
>foreach</A
>). In PHP3, you
can combine <A
HREF="control-structures.while.html"
>while</A
>
with the <A
HREF="function.list.html"
><B
CLASS="function"
>list()</B
></A
> and <A
HREF="function.each.html"
><B
CLASS="function"
>each()</B
></A
>
functions to achieve the same effect. See the documentation for
these functions for an example.
</P
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