php While 循环和多个条件
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While Loops and Multiple Conditions
提问by jason328
Is it possible to write multiple conditions in a while loop? If not, what is an alternative? I tried it and was returned with an error relating the line of code that sets up the conditions for the while loop. Here is an example of what I mean.
是否可以在 while 循环中编写多个条件？如果没有，有什么替代方案？我尝试了它并返回一个错误，该错误与设置 while 循环条件的代码行有关。这是我的意思的一个例子。
$s = 1;
while ($result_row = mysql_fetch_assoc($query) && $s < 5)
{
echo $result_row['id'];
$s++;
}
回答by Mark Byers
That is possible, but because =has lower precedencethan &&you need parentheses to ensure that your statement is interpreted correctly:
这是可能的，但由于=具有较低的优先级比&&你需要括号以确保您的语句是正确解释：
while (($result_row = mysql_fetch_assoc($query)) && ($s < 5))
The parentheses around $s < 5are not required here, but I've included them for clarity.
$s < 5此处不需要括号，但为了清楚起见，我将它们包括在内。
However it would be easier just to modify your query to only return 5 rows, by adding LIMIT 5.
但是，通过添加LIMIT 5.
SELECT ...
FROM yourtable
ORDER BY ...
LIMIT 5
回答by JoeTomato
You could try:
你可以试试：
$s=1
while ($result_row = mysql_fetch_assoc($query))
{
echo $result_row['id'];
$s++;
if($s>5){
break;
}
}
回答by Ibrahim Azhar Armar
while i see nothing wrong in that. the other way round is to do something like this.
虽然我认为这没有错。另一种方式是做这样的事情。
$s = 1;
while ($result_row = mysql_fetch_assoc($query))
{
if($s < 5) {
//enter the condition
}
$s++;
}
回答by Mike Christensen
The value of $result_rowis probably being set to the Boolean condition of whether mysql_fetch_assoc($query)returns something true-ish and $sis less than 5. So trying to read $result_rowas a dictionary no longer works.
的值$result_row可能被设置为是否mysql_fetch_assoc($query)返回真实值的布尔条件并且$s小于 5。因此尝试将其$result_row作为字典阅读不再有效。
You can use parenthesis to specify exactly how things get parsed:
您可以使用括号来准确指定解析内容的方式：
while (($result_row = mysql_fetch_assoc($query)) && ($s < 5))
This way, $result_rowgets set to mysql_fetch_assoc($query), which is what you want, andthe loop continues as long as the logical value of that assignment returns something true-ish, as well as sis less than 5.
这样一来，$result_row被设置为mysql_fetch_assoc($query)，这是你想要的东西，并循环继续，只要该转让收益东西真十岁上下的逻辑值，以及s小于5。
