Binary operator '+' cannot be applied to operands of type 'Int' and 'Double'

Just use the Double() function to initialize a Double value with the integer value.

import UIKit

let myInt : Int = 111
let myDouble : Double = 222.222

//Incorrect addition of Integer and Double
print(String(format: "%.9f", myInt + myDouble))

//Correct Way to add Integer and Double
print(String(format: "%.9f", Double(myInt) + myDouble))
//Result = 333.222000000