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How to multiply an int and a double

Written by Paul Hudson    @twostraws

Swift’s type safety means code to multiply an integer and a double won’t compile:

let a = 4
let b = 5.0
let c = a * b

You can either fix this by forcing your integer to be a double:

let a: Double = 4
let b = 5.0
let c = a * b

Alternatively you can convert your integer to a double as needed:

let a = 4
let b = 5.0
let c = Double(a) * b

If this situation really annoys you and you want it solved fully, add this custom * function:

func *(lhs: Int, rhs: Double) -> Double {
    return Double(lhs) * rhs

That will multiply an integer on the left with a double on the right, returning a double containing the result.

Available from iOS 8.0

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This is part of the Swift Knowledge Base, a free, searchable collection of solutions for common iOS questions.

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