---
title: "+=(_:_:)"
framework: swift
role: symbol
role_heading: Operator
path: "swift/double/+=(_:_:)"
---

# +=(_:_:)

Adds two values and stores the result in the left-hand-side variable, rounded to a representable value.

## Declaration

```swift
static func += (lhs: inout Double, rhs: Double)
```

## Parameters

- `lhs`: The first value to add.
- `rhs`: The second value to add.