IF STATEMENT ALWAYS RETURNS TRUE?

Anon

I have an if statement that is always returning true, even when it definitely isn't. It is basically displaying something in a table, either as a text box, or as just the value. Every time it displays the true value, whatever the value of $recordstatus is. Does anyone know why it won't produce the false value at all? I've tried swapping it round, but no luck. It runs through the parser fine.

It goes as follows:

<?php

for ($counter = 0; $counter < $row; $counter++) {

$recordstatus = mysql_result($result,$counter,"status");

if $recordstatus = 'DESPATCHED' {
echo mysql_result($result,$counter,"contact");
}
else
{
?>
<input type="text" name="contact" value="<?php echo mysql_result($result,$counter,"contact") ?>@>
<?php
}
}
?>

thanks

Anon

The manual doesn't say "always use parentheses," but the examples do. I'm not entirely sure what the parser does to your code without the test case being enclosed in parentheses.

Also, did you intend to test whether 'DESPATCHED' is true while assigning its value to $recordstatus, or did you intend to test whether $recordstatus is already equal to 'DESPATCHED'? Your example

if $recordstatus = 'DESPATCHED'

could have been intended to read

if ($recordstatus = 'DESPATCHED')

... which assigns the value and tests the result, or

if ($recordstatus == 'DESPATCHED')

... which tests the result of a comparison.

Anon

Yes, sorry, I just forgot the () in this message!

I'm actually checking whether $recordstatus is equal to DESPATCHED, not assigning it. So I think the == is the answer, is that right?

So if I put

if ($recordstatus =='DESPATCHED') {

true

}
else
{
false expression
}

It will work correctly?

Thanks for your help.

Regards

Elizabeth

Anon

Right.

Whenever you see "==" it's a test; think of it as an interrogative "is equal to?"

PHP borrowed this construct from C, and it's probably the Number One mistake of new C users.

But it's a good construct, as it eliminates any ambiguity between an assignment and a comparison.

Anon

Ah, yes. I'm more pascal myself, so I'm used to

:= when you assign to variable
= for comparison

Got quite confused there.

Thanks again.

Regards

Elizabeth

Anon

Also, did you intend to test whether 'DESPATCHED' is true
while assigning its value to $recordstatus, or did you intend
to test whether $recordstatus is already equal to 'DESPATCHED'?
Your example

    if $recordstatus = 'DESPATCHED'

That's pretty easy to sort out from the context! It's "never"
necessary to test the assignment of a contstant because,
as Elizabeth has inadvertantly discovered, the result is
always true. What does sometimes make sense is to say

    if ($recordstatus = $newstatus)

As far as spotting this particular error, perhaps we should
propose a rule that nobody gets to program in PHP until
they have at least a working knowledge of C? This wouldn't
prevent the programmer from accidentally making the mistake
(please don't ask me how I know) but at least the old C hand
knows what is going on when it bites him/her.

Or perhaps some enterprising soul could write Lint for PHP?

Anon

Whoa ...

".. the result is always true."

Nope. The result of an assignment is the assigned value, which might be true or false. ($foo = 0) has a value of 0, which is false. ($foo = 1) has a value of 1, which is true. Et cetera.

<?
if ($foo = 0) echo "success";
else echo "failure";
?>

There are occasions when this behavior is useful, as in:

if ($validuser = isloggedin()) / do something /;

This sets $validuser to the returned value of isloggedin(); later in the program you can branch on $validuser without having to call the function again.

Anon

Oh, but you missed where I said

  to test the assignment of a <b>constant</b>

In that case, you know that the result will never be false
(except, of course, if the constant is 'false', in which
case you know the result will never be true.)

Not to mention I specifically said testing the result of an
assignment where the RHS is not a constant is useful...