"The standard arithmetic operators are available in PHP and
these are the same as in any other language:

+ Addition of numbers (20+10)
- Subtraction of numbers (20-10)
* Multiplication of numbers (20*10)
/ Division of numbers (20/10)

"When setting up or assigning variables, you can set the initial
value to the result of a mathematical equation, as in the following
example:

$result = 2+2; // $result will be equal to 4

For subtraction and addition there's also a very handy shortcut
or two which are great for loop handling, these shortcuts are used
by appending either a double + or a double - after the variable
name:

$a = 1; // $a equals to 1
$a++; // $a equals 2
$a--; // $a once again equals 1