Negative Numbers in PHP

Numbers can be negative. To do this, a minus sign must be placed in front of the number:

<?php
	$a = -1;
	echo $a; // will output -1
?>

The minus sign can be applied to both numbers and variables:

<?php
	$a = 1;
	$b = -$a; // wrote to $b the contents of $a with the opposite sign
	echo $b;  // will output -1
?>

Or like this:

<?php
	$a = 1;
	echo -$a; // will output -1
?>

Create a variable $a with the value -100. Display this value on the screen.

Create a variable $a, write any positive or negative number into it. Display this number with the opposite sign on the screen.