An alternative and very useful syntax is the following one:
statement ? execute if true : execute if false
Ths is very usefull for dynamic outout inside strings, for example:
print('$a is ' . ($a > $b ? 'bigger than' : ($a == $b ? 'equal to' : 'smaler than' )) . ' $b');
This will print "$a is smaler than $b" is $b is bigger than $a, "$a is bigger than $b" if $a si bigger and "$a is equal to $b" if they are same.
else
(PHP 4, PHP 5, PHP 7, PHP 8)
Souvent, vous voulez exécuter une instruction si une
condition est remplie et une autre instruction si cette condition
n'est pas remplie. C'est à cela que sert else.
else fonctionne après un
if et exécute les instructions
correspondantes au cas où l'expression du if
est false. Dans l'exemple suivant, ce bout de code
affiche a est plus grand que b si la
variable $a est plus grande que la variable
$b, et a est plus petit que b
sinon :
<?php
if ($a > $b) {
echo "a est plus grand que b";
} else {
echo "a est plus petit que b";
}
?>else ne sont
exécutées que si l'expression du if
est false, et s'il existe des expressions elseif
- uniquement si elles sont également évaluées à false (voir elseif).
Note: Dangling else
Dans le cas d'instructions
if-elseimbriquées, unelseest toujours associé avec leifle plus proche.Malgré l'indentation (qui n'a pas d'importance en PHP), le<?php
$a = false;
$b = true;
if ($a)
if ($b)
echo "b";
else
echo "c";
?>elseest associé avec leif ($b), ainsi cet exemple ne produit pas de sortie. Tant bien que s'appuyer sur ce comportement est valide, il est recommandé de l'éviter en utilisant des accolades pour résoudre toute ambiguïté possible.
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User Contributed Notes 2 notes
dormeydo at gmail dot com ¶
16 years ago
Caliban Darklock ¶
20 years ago
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.
