Negative Numbers in PHP

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

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

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

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