(PHP 4, PHP 5, PHP 7, PHP 8)
Muitas vezes deseja-se executar uma instrução se uma certa condição
for válida, e uma instrução diferente se a mesma condição não for válida. Para isso
que o else serve. O else
estende a instrução if para executar outras
caso a expressão no if retornar
false. Por exemplo, o código a
seguir exibirá a is greater than
b se $a for maior que
$b, e a is NOT greater
than b caso contrário:
<?php
if ($a > $b) {
echo "a is greater than b";
} else {
echo "a is NOT greater than b";
}
?>else só é executada se a
expressão de avaliação do if for avaliada como
false, e se tiver qualquer expressão
elseif - somente se também retornarem
false (veja elseif).
Nota: Else pendurado
Em caso de declarações
if-elseaninhadas, umelseé sempre associado com oifmais próximo.Apesar da indentação (o que não importa para o PHP), o<?php
$a = false;
$b = true;
if ($a)
if ($b)
echo "b";
else
echo "c";
?>elseé associado com oif ($b), então o exemplo não produz nenhuma saída. Embora seja válido confiar nesse comportamento, é recomendado evitá-lo usando chaves para resolver ambiguidades em potencial.
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.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.