Changing the sign of a number in PHP?

php math numbers sign

137,854

Solution 1

A trivial

$num = $num <= 0 ? $num : -$num ;

or, the better solution, IMHO:

$num = -1 * abs($num)

As @VegardLarsen has posted,

the explicit multiplication can be avoided for shortness but I prefer readability over shortness

I suggest to avoid if/else (or equivalent ternary operator) especially if you have to manipulate a number of items (in a loop or using a lambda function), as it will affect performance.

"If the float is a negative, make it a positive."

In order to change the sign of a number you can simply do:

$num = 0 - $num;

or, multiply it by -1, of course :)

Solution 2

$float = -abs($float);

Solution 3

How about something trivial like:

inverting:
```
$num = -$num;
```
converting only positive into negative:
```
if ($num > 0) $num = -$num;
```
converting only negative into positive:
```
if ($num < 0) $num = -$num;
```

Solution 4

re the edit: "Also i need a way to do the reverse If the float is a negative, make it a positive"

$number = -$number;

changes the number to its opposite.

Solution 5

I think Gumbo's answer is just fine. Some people prefer this fancy expression that does the same thing:

$int = (($int > 0) ? -$int : $int);

EDIT: Apparently you are looking for a function that will make negatives positive as well. I think these answers are the simplest:

/* I am not proposing you actually use functions called
   "makeNegative" and "makePositive"; I am just presenting
   the most direct solution in the form of two clearly named
   functions. */
function makeNegative($num) { return -abs($num); }
function makePositive($num) { return abs($num); }

View more solutions

137,854

Author by

dotty

Hmm not alot really.

Updated on July 05, 2022

Comments

dotty almost 2 years
I have a few floats:
```
-4.50
+6.25
-8.00
-1.75
```
How can I change all these to negative floats so they become:
```
-4.50
-6.25
-8.00
-1.75
```
Also I need a way to do the reverse

If the float is a negative, make it a positive.
drAlberT over 14 years

Ops, yes sorry, just reversed the order:)
Dan Tao over 14 years

Ha, ok... for a second there I was doubting my own sanity.
Gumbo over 14 years

Why should getting the absolute value of a variable, inverting it and reassigning it to that variable no matter what value it is be more performant?
drAlberT over 14 years

maybe it is not, you are right. It would depend on the number of already OK numbers :)
Gumbo over 14 years

-1 -1 * (0 - $num) is equal to (-1 * 0) - (-1 * $num) is equal to 1 * $num.
Dan Tao over 14 years

Your last answer is not correct! If $num is positive then -1 * (0 - $num) will return a positive number.
drAlberT over 14 years

I just realized it, my bad sorry, removed ! Thank you
drAlberT over 14 years

You are right, but it would be performed at low level, in C. By PHP, not in PHP.
drAlberT over 14 years

why to wrap abs() when used as is? nah.
Frederik Krautwald over 7 years

Thanks for commenting why you downvoted. Really useful.
Progrock almost 6 years

I think this is because the OP originally stated that they only want positive numbers to flip sign. But the question is rather confusing with the ambiguous bolt on: "Also I need a way to do the reverse".
ReSpawN almost 6 years

In my case the $num = 0 - $num was exactly what I needed. The one 'account' looses 100, the other 'gains' 100, which needs to be 'toggled', as it were.
ReSpawN almost 6 years

"Also I need a way to do the reverse", this answer only does one thing...
Frits almost 5 years

@ReSpawN To be fair, the reverse is literally just taking the - away. i.e. $float = abs($float);
ShivarajRH over 4 years

value always will be negative. expected to mention it.
B001ᛦ almost 3 years

Please add a proper explanation to your answer. Also mention that your solutio needs to install an extra extension.
Eskay Amadeus almost 2 years

Installing an entire extension just to use a method isn't really worth it. But if the developer has other needs that the extension can satisfy, then it's a good option.