if
Yes, that code is clearly ambiguous. I would think that the code does the 'right thing' with it anyway. The else should bind to the nearest if.
If you are going to nest ifs, use curly brackets and stay sane.
<?
if ($a == 1)
{ /* nested if */
if ($b == 2) echo '2';
} else
/* other code */
?>
else
(PHP 4, PHP5)
Oft will man eine Anweisung ausführen, wenn eine bestimmte Bedingung erfüllt ist, und eine andere Anweisung, wenn dies nicht der Fall ist. Dies ist der Einsatzzweck von else. else erweitert eine if-Anweisung um eine weitere Anweisung, die dann ausgeführt werden soll, wenn der Ausdruck in der if-Anweisung zu FALSE ausgewertet wird. Der folgende Programmcode würde z.B. a ist größer als b ausgeben, wenn $a größer als b ist, ansonsten a ist NICHT größer als b
<?php
if ($a > $b) {
echo "a ist größer als b";
} else {
echo "a ist NICHT größer als b";
}
?>
add a note
User Contributed Noteselse
robbak
21-Jun-2007 09:54
21-Jun-2007 09:54
jsimlo
15-Aug-2006 04:30
15-Aug-2006 04:30
This generates a parser error:
<?
if ($a == 1):
/* nested if */
if ($b == 2) echo '2';
else:
/* other code */
endif;
?>
The nested "if" binds the outer "else" and the colon then generates a parser error.
As this "bug" is not going to be fixed (see http://bugs.php.net/bug.php?id=838), this could be an artful solution to this problem:
<?
if ($a == 1):
/* nested if */
if ($b == 2) echo '2';
/* dummy expression */
;
else:
/* other code */
endif;
?>
gwmpro at yahoo dot com
04-May-2006 05:00
04-May-2006 05:00
I am new to this language. It seems to me that only the semicolon ';' is required, the brackets '{}' are not if there is only one statement. The code segment below would be legal.
<?php
if ($a > $b)
echo "a is bigger than b";
else
echo "a is NOT bigger than b";
?>
Caliban Darklock
08-Nov-2004 08:24
08-Nov-2004 08:24
If you're coming from another language that does not have the "elseif" construct (e.g. C++), it's important to recognise that "else if" is a nested language construct and "elseif" is a linear language construct; they may be compared in performance to a recursive loop as opposed to an iterative loop.
<?php
$limit=1000;
for($idx=0;$idx<$limit;$idx++)
{ $list[]="if(false) echo \"$idx;\n\"; else"; }
$list[]=" echo \"$idx\n\";";
$space=implode(" ",$list);| // if ... else if ... else
$nospace=implode("",$list); // if ... elseif ... else
$start=array_sum(explode(" ",microtime()));
eval($space);
$end=array_sum(explode(" ",microtime()));
echo $end-$start . " seconds\n";
$start=array_sum(explode(" ",microtime()));
eval($nospace);
$end=array_sum(explode(" ",microtime()));
echo $end-$start . " seconds\n";
?>
This test should show that "elseif" executes in roughly two-thirds the time of "else if". (Increasing $limit will also eventually cause a parser stack overflow error, but the level where this happens is ridiculous in real world terms. Nobody normally nests if() blocks to more than a thousand levels unless they're trying to break things, which is a whole different problem.)
There is still a need for "else if", as you may have additional code to be executed unconditionally at some rung of the ladder; an "else if" construction allows this unconditional code to be elegantly inserted before or after the entire rest of the process. Consider the following elseif() ladder:
<?php
if($a) { conditional1(); }
elseif($b) { conditional2(); }
elseif($c) { conditional3(); }
elseif($d) { conditional4(); }
elseif($e) { conditional5(); }
elseif($f) { conditional6(); }
elseif($g) { conditional7(); }
elseif($h) { conditional8(); }
else { conditional9(); }
?>
To insert unconditional preprocessing code for $e onward, one need only split the "elseif":
<?php
if($a) { conditional1(); }
elseif($b) { conditional2(); }
elseif($c) { conditional3(); }
elseif($d) { conditional4(); }
else {
....unconditional();
....if($e) { conditional5(); }
....elseif($f) { conditional6(); }
....elseif($g) { conditional7(); }
....elseif($h) { conditional8(); }
....else { conditional9(); }
}
?>
The alternative is to duplicate the unconditional code throughout the construct.
cap at capsi dot com
06-Oct-2000 07:58
06-Oct-2000 07:58
Often you can avoid large if/else statements in your code by using the ternary operator. For example:
<?php
echo "You have $i ". ($i==1 ? "message" : "messages"). " in your mailbox.\n";
?>