###### Hai Huang

12,675 Points# Why are the unary operators unary operators?

(Maybe the title is a little stupid..)

I completely understand the usages of the unary operators introduced in this video, but some of them seem to me binary operators.

Let's say for an example.

var a: Int = 1

a += 1 a -= 1

In the two lines above, both "+=" and "-=" seem to me binary operators because they connect two operands (a and 1) and are located in between as infix.

Well, the negating operator (var a: Bool = true; a = !a) is for me a unary operator because it only affects one operand (a).

## 1 Answer

###### Michael Hulet

Treehouse Moderator 47,742 PointsYour concept of unary and binary operators is correct. I don't know why the mathematical assignment operators were listed as unary operators in this video, because they're actually binary operators, as you suspected. There are only 3 unary operators in Swift by default:

- The logical negation operator (
`!`

). This inverts a boolean expression, so`!true`

is`false`

, and`!false`

is`true`

- The mathematical negation operator (
`-`

). This makes a positive number negative, and a negative number positive (example:`-42`

) - The unary plus operator (
`+`

). This simply returns its value as is. For example`+42`

is still just`42`

. This operator is entirely useless, but looks nice near a mathematical negation operator when you're choosing if you want something positive or negative