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PHP : Language Reference : Control Structures : else

else

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";
}
?>

The else statement is only executed if the if expression evaluated to FALSE, and if there were any elseif expressions - only if they evaluated to FALSE as well (see elseif).

Related Examples ( Source code ) » control_structures.else
















Code Examples / Notes » control_structures.else

robbak

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 */
?>


jsimlo

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;
?>


cap

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";
?>


caliban darklock

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.


gwmpro

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";
?>


mitch

At gwmpro at yahoo dot com
The curly brace is not required however, for readability and maintenance, many developers would consider it bad style not to include them.


ravi dot goglobium

another good example of using ternary operator is
<?php
$a = 20;
$b = 30;
$c = 70;
echo ($a > $b && $a > $c) ? $a : ($b > $a && $b > $c) ? $b : $c;
?>


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