Control Structures
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;
?>
Often you'd want to execute a statement if a certain condition is
met, and a different statement if the condition is not met. This
is what else is for. else
extends an if statement to execute a statement
in case the expression in the if statement
evaluates to FALSE. For example, the following
code would display a is bigger than
b if $a is bigger than
$b, and a is NOT bigger
than b otherwise:
<?php
if ($a > $b) {
echo "a is bigger than b";
} else {
echo "a is NOT bigger than b";
}
?>
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User Contributed Noteselse
jsimlo
15-Aug-2006 02:30
15-Aug-2006 02:30
gwmpro at yahoo dot com
04-May-2006 03:00
04-May-2006 03:00
I am new to this language. It seems to me that only the semicolon ';' is required, the brackets '{}' are not if there is only one statement. The code segment below would be legal.
<?php
if ($a > $b)
echo "a is bigger than b";
else
echo "a is NOT bigger than b";
?>
Caliban Darklock
08-Nov-2004 07:24
08-Nov-2004 07:24
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 05:58
06-Oct-2000 05:58
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";
?>