else
Colon syntax: The boxed text says that "else if" (two words) is required, but the examples just below the box show "else if" as incorrect and "elseif" as correct.
elseif
elseif, както подсказва и името й, е комбинация от if и else. Също както else, тя разширява конструкцията if така, че да изпълни различна инструкция, в случай че първоначалният израз if се е изчислил на FALSE. За разлика от else обаче тя ще изпълни този алтернативен израз само ако условният израз elseif се изчислява на TRUE. Например, следният код ще изведе a е по-голямо от b, a е равно на b или a е по-малко от b:
<?php
if ($a > $b) {
echo "a е по-голямо от b";
} elseif ($a == $b) {
echo "a е равно на b";
} else {
echo "a е по-малко от b";
}
?>
В рамките на една конструкция if може да има много elseif-ове. Първият израз elseif (ако има такъв), който се изчисли на TRUE ще бъде изпълнен. В PHP можете също да напишете и 'else if' (с две думи) и поведението му ще бъде идентично на 'elseif' (с една дума). Синтактичното значение е малко по-различно (ако сте запознати със C, тук е налице същото поведение), но последният ред е този, който и в двата случая ще има абсолютно същото поведение.
Конструкцията elseif се изпълнява само ако предшестващият израз if и всички предшестващи изрази elseif се изчислят на FALSE и текущият израз elseif се е изчислил на TRUE.
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User Contributed Noteselseif
cbuck at usna dot edu
02-Jul-2008 10:32
02-Jul-2008 10:32
01-Feb-2007 06:54
There is no good way to interpret the dangling else. One must pick a way and apply rules based on that.
Since there is no endif before an else, there is no easy way for PHP to know what you mean.
Vladimir Kornea
28-Dec-2006 01:59
28-Dec-2006 01:59
The parser doesn't handle mixing alternative if syntaxes as reasonably as possible.
The following is illegal (as it should be):
<?
if($a):
echo $a;
else {
echo $c;
}
?>
This is also illegal (as it should be):
<?
if($a) {
echo $a;
}
else:
echo $c;
endif;
?>
But since the two alternative if syntaxes are not interchangeable, it's reasonable to expect that the parser wouldn't try matching else statements using one style to if statement using the alternative style. In other words, one would expect that this would work:
<?
if($a):
echo $a;
if($b) {
echo $b;
}
else:
echo $c;
endif;
?>
Instead of concluding that the else statement was intended to match the if($b) statement (and erroring out), the parser could match the else statement to the if($a) statement, which shares its syntax.
While it's understandable that the PHP developers don't consider this a bug, or don't consider it a bug worth their time, jsimlo was right to point out that mixing alternative if syntaxes might lead to unexpected results.
phpprogrammer at artspad dot net
11-Aug-2006 01:58
11-Aug-2006 01:58
The comment critizing matheo's code while making some perhaps interesting statements about code efficiency missed the point completely.
echo 0; is different then echo false;
echo 0 will print a 0
echo false will print nothing.
So, the ternary operator technique was simply assuring there would be a displayable value.
If anything matheo showed prowess as a programmer and that he was knowledgable about nuances in php programming by knowing how to use the ternary operator to provide values true and false that are displayable.
Perhaps a clearer example of this would have been:
$is_a_bigger = ($a > $b) ? "true" : "false" ;
It is true that the result of a logic expression is a value like any other, it is a value though of a specific type which if using === can be checked for boolean logic which may or may not be what a programmer wants.
The general caveat if we are going to pontificate to programmers is to know exacly what you are getting from any operation and know the consequences of doing so. Which I think matheo knew quite well, and appropriately accounted for.