[RESOLVED] Retaining Value of a Ceil-ed Function

aquastream

Okay, here's a newbie theoretical question. In other words, something I've come across which I have no idea why I would ever use but I'm curious about it anyway!

If i add a number to a variable, the answer to this becomes the new value of that variable, and if I subtracted a number from the variable, it would then subtract it from the new value rather than the original value.

For example:

<?php
$variable1 = 2;
$variable1 += 4; echo $variable1."<br />";
$variable1 -= 1; echo $variable1;
?>

However, when I use either a ceil or floor function to a float, the rounded value doesn't behave like the previous example. Instead, when I do a mathematical function to the variable, it takes it from the original value rather than the new ceil-ed or floor-ed value.

For example:

<?php
$variable1 = 3.14;
echo ceil($variable1)."<br />";
$variable1 += 1; echo $variable1
?>

Is the reason for this something to do with the fact that ceil and floor aren't pure mathematical functions like adding or squaring? If I wanted to in the previous example retain the value of the ceil (4) when adding to its value, how would I do this?

PS: Brownie points to anyone who can come up with a reason as to why I would do this in a real project.

laserlight

aquastream wrote:
However, when I use either a ceil or floor function to a float, the rounded value doesn't behave like the previous example. Instead, when I do a mathematical function to the variable, it takes it from the original value rather than the new ceil-ed or floor-ed value.

If you read the PHP manial entry for [man]ceil/man, you will see that it "returns the next highest integer value by rounding up value if necessary". So, ir returns the new value, but does not change the value of its argument.

aquastream wrote:
Is the reason for this something to do with the fact that ceil and floor aren't pure mathematical functions like adding or squaring? If I wanted to in the previous example retain the value of the ceil (4) when adding to its value, how would I do this?

No. Consider taking the square root... that sounds like a "pure mathematical function" to me:

<?php
$variable1 = 4;
echo sqrt($variable1) . '<br />';
echo $variable1;
?>

On the other hand, consider the use of my nifty laser_ceil function:

<?php
function laser_ceil(&$value)
{
    $value = ceil($value);
    return $value;
}

<?php
$variable1 = 3.14;
echo laser_ceil($variable1) . "<br />";
$variable1 += 1;
echo $variable1;
?>

aquastream wrote:
PS: Brownie points to anyone who can come up with a reason as to why I would do this in a real project.

Do what?

aquastream

laserlight;10941692 wrote:
If you read the PHP manial entry for ceil(), you will see that it "returns the next highest integer value by rounding up value if necessary". So, ir returns the new value, but does not change the value of its argument.

Thanks. That explains why changing the ceiling doesn't inherently change the value of the variable.

laserlight;10941692 wrote:
No. Consider taking the square root... that sounds like a "pure mathematical function" to me.

I think I might have been a little vague when talking about a "pure mathematical function". I agree with you that taking the square root would be a pure mathematical function if there was one. I was just speculating as to why ceil didn't do the same thing as adding or squaring, and I made the guess that it was because that unlike adding or squaring, you can't express rounding in mathematical syntax. Therefore, that was what I meant when I refered to "pure mathematical functions"

laserlight;10941692 wrote:
On the other hand, consider the use of my nifty laser_ceil function

Nifty, and it works.

Also when I mentioned brownie points, I wanted to know of any reason why you'd use this type of code in a real project. I'm a newbie, so while I can get the theory behind it, its kind of hard to picture why I'd actually want to retain the value of the ceil and then add another number to it. My guess is that PHP at this level is so simple that it barely has any practical applications, but I just thought I'd ask.

Thanks for your help Laserlight!

laserlight

aquastream wrote:
I was just speculating as to why ceil didn't do the same thing as adding or squaring, and I made the guess that it was because that unlike adding or squaring, you can't express rounding in mathematical syntax.

There is common mathematical notation to express ceiling and floor functions, though I do not know of any particular notation for rounding to the nearest integer.

aquastream wrote:
Also when I mentioned brownie points, I wanted to know of any reason why you'd use this type of code in a real project. I'm a newbie, so while I can get the theory behind it, its kind of hard to picture why I'd actually want to retain the value of the ceil and then add another number to it. My guess is that PHP at this level is so simple that it barely has any practical applications, but I just thought I'd ask.

Well, you would know when the time comes 🙂

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