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# In the editor you've been provided with two classes - Point to represent a coordinate point and Machine. The machine has

I don't get why i am getting compiler error?

robots.swift
```class Point {
var x: Int
var y: Int

init(x: Int, y: Int) {
self.x = x
self.y = y
}
}

class Machine {
var location: Point

init() {
self.location = Point(x: 0, y: 0)
}

func move(_ direction: String) {
print("Do nothing! Im a machine!")
}
}

class Robot: Machine {
override func move(_ direction: String) {
switch direction {
case "Up": location.y ++

case "Down": location.y --

case "Left": location.x --

case "Right": location.x ++

default: break
}
}
}
```

## 2 Answers

The ++ and -- operators are not supported in Swift 3. If you want to increase or decrease a variable using shorthand you have to use `+= 1` or `-= 1` instead, like this:

```class Point {
var x: Int
var y: Int

init(x: Int, y: Int) {
self.x = x
self.y = y
}
}

class Machine {
var location: Point

init() {
self.location = Point(x: 0, y: 0)
}

func move(_ direction: String) {
print("Do nothing! Im a machine!")
}
}

class Robot: Machine {
override func move(_ direction: String) {
switch direction {
case "Up": location.y += 1

case "Down": location.y -= 1

case "Left": location.x -= 1

case "Right": location.x += 1

default: break
}
}
}
```

Then your code will work.