# Arithmetic and Logical Operators

An *operator* is a type of expression that transforms or combines one or more
other expressions. Operators either combine two values in some way to
produce a third result value, or transform a single given value to
produce a single result.

Operators that work on two values place an operator symbol between the two
values, similar to mathematical notation: `1 + 2`

. Operators that work on
only one value place an operator symbol before that value, like
`!true`

.

The Terraform language has a set of operators for both arithmetic and logic, which are similar to operators in programming languages such as JavaScript or Ruby.

When multiple operators are used together in an expression, they are evaluated in the following order of operations:

Use parentheses to override the default order of operations. Without
parentheses, higher levels will be evaluated first, so Terraform will interpret
`1 + 2 * 3`

as `1 + (2 * 3)`

and *not* as `(1 + 2) * 3`

.

The different operators can be gathered into a few different groups with similar behavior, as described below. Each group of operators expects its given values to be of a particular type. Terraform will attempt to convert values to the required type automatically, or will produce an error message if automatic conversion is impossible.

## Arithmetic Operators

The arithmetic operators all expect number values and produce number values as results:

`a + b`

returns the result of adding`a`

and`b`

together.`a - b`

returns the result of subtracting`b`

from`a`

.`a * b`

returns the result of multiplying`a`

and`b`

.`a / b`

returns the result of dividing`a`

by`b`

.`a % b`

returns the remainder of dividing`a`

by`b`

. This operator is generally useful only when used with whole numbers.`-a`

returns the result of multiplying`a`

by`-1`

.

Terraform supports some other less-common numeric operations as
functions. For example, you can calculate exponents
using
the `pow`

function.

## Equality Operators

The equality operators both take two values of any type and produce boolean values as results.

`a == b`

returns`true`

if`a`

and`b`

both have the same type and the same value, or`false`

otherwise.`a != b`

is the opposite of`a == b`

.

Because the equality operators require both arguments to be of exactly the same type in order to decide equality, we recommend using these operators only with values of primitive types or using explicit type conversion functions to indicate which type you are intending to use for comparison.

Comparisons between structural types may produce surprising results if you
are not sure about the types of each of the arguments. For example,
`var.list == []`

may seem like it would return `true`

if `var.list`

were an
empty list, but `[]`

actually builds a value of type `tuple([])`

and so the
two values can never match. In this situation it's often clearer to write
`length(var.list) == 0`

instead.

## Comparison Operators

The comparison operators all expect number values and produce boolean values as results.

`a < b`

returns`true`

if`a`

is less than`b`

, or`false`

otherwise.`a <= b`

returns`true`

if`a`

is less than or equal to`b`

, or`false`

otherwise.`a > b`

returns`true`

if`a`

is greater than`b`

, or`false`

otherwise.`a >= b`

returns`true`

if`a`

is greater than or equal to`b`

, or`false`

otherwise.

## Logical Operators

The logical operators all expect bool values and produce bool values as results.

`a || b`

returns`true`

if either`a`

or`b`

is`true`

, or`false`

if both are`false`

.`a && b`

returns`true`

if both`a`

and`b`

are`true`

, or`false`

if either one is`false`

.`!a`

returns`true`

if`a`

is`false`

, and`false`

if`a`

is`true`

.

Terraform does not have an operator for the "exclusive OR" operation. If you
know that both operators are boolean values then exclusive OR is equivalent
to the `!=`

("not equal") operator.