Changing the sign of a number in PHP?

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.

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 :)

$float = -abs($float);

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;
  

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.

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); }

function positive_number($number)
{
    if ($number < 0) {
        $number *= -1;
    }

   return $number;
}

function invertSign($value)
{
    return -$value;
}

gmp_neg — Negate number

is a PHP function since version 4, that allows you to negate a number, under the GMP PHP API. you can learn more here https://www.php.net/manual/en/ref.gmp.php

<?php
$neg1 = gmp_neg("1");
echo gmp_strval($neg1) . "\n";
$neg2 = gmp_neg("-1");
echo gmp_strval($neg2) . "\n";
?>

using alberT and Dan Tao solution:

negative to positive and viceversa

$num = $num <= 0 ? abs($num) : -$num ;