(PHP 4, PHP 5, PHP 7, PHP 8)
A menudo, se desea ejecutar una sentencia si una
condición se cumple y otra sentencia si esta condición
no se cumple. Para esto se utiliza else.
else funciona después de un
if y ejecuta las sentencias
correspondientes en caso de que la expresión del if
sea false. En el siguiente ejemplo, este fragmento de código
muestra a es más grande que b si la
variable $a es más grande que la variable
$b, y a es más pequeño que b
en caso contrario:
<?php
if ($a > $b) {
echo "a es más grande que b";
} else {
echo "a es más pequeño que b";
}
?>else solo se
ejecutan si la expresión del if
es false, y si existen expresiones elseif
- solo si también se evalúan como false (ver elseif).
Nota: Dangling else
En el caso de sentencias
if-elseanidadas, unelsesiempre se asocia con elifmás cercano.A pesar de la indentación (que no tiene importancia en PHP), el<?php
$a = false;
$b = true;
if ($a)
if ($b)
echo "b";
else
echo "c";
?>elsese asocia con elif ($b), por lo que este ejemplo no produce ninguna salida. Aunque apoyarse en este comportamiento es válido, se recomienda evitarlo utilizando llaves para resolver cualquier posible ambigüedad.
An alternative and very useful syntax is the following one:statement ? execute if true : execute if falseThs 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 $b" if they are same.If you're coming from another language that does not have the "elseif" construct (e.g. C++), it's important to recognise that "else if" is a nested language construct and "elseif" is a linear language construct; they may be compared in performance to a recursive loop as opposed to an iterative loop. <?php$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 $limit will also eventually cause a parser stack overflow error, but the level where this happens is ridiculous in real world terms. Nobody normally nests if() blocks to more than a thousand levels unless they're trying to break things, which is a whole different problem.)There is still a need for "else if", as you may have additional code to be executed unconditionally at some rung of the ladder; an "else if" construction allows this unconditional code to be elegantly inserted before or after the entire rest of the process. Consider the following elseif() ladder:<?phpif($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 $e onward, one need only split the "elseif":<?phpif($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.