CascadiaPHP 2024

else

(PHP 4, PHP 5, PHP 7, PHP 8)

Con frecuencia se desea ejecutar una sentencia si una determinada condición se cumple y una sentencia diferente si la condición no se cumple. Esto es para lo que sirve else. El else extiende una sentencia if para ejecutar una sentencia en caso que la expresión en la sentencia if se evalúe como false. Por ejemplo, el siguiente código deberá mostrar a es mayor que b si $a es mayor que $b y a NO es mayor que b en el caso contrario:

<?php
if ($a > $b) {
echo
"a es mayor que b";
} else {
echo
"a NO es mayor que b";
}
?>
La sentencia else sólo es ejecutada si la expresión if es evaluada como false y si hay algunas expresiones elseif - sólo se ejecuta si también todas son evaluadas como false (ver elseif).

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User Contributed Notes 2 notes

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24
dormeydo at gmail dot com
16 years ago
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.
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12
Caliban Darklock
19 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.
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