数据类型转换

//: Playground - noun: a place where people can play

import UIKit

/*
 Swift中不存在隐式类型转换，所有的类型转换都必须是显式的
 */

let num1 = 10
let num2 = 9.9
let intSum = num1 + Int(num2)
let doubleSum = Double(num1) + num2

// 明确说明是什么数据类型
let num3:Int = 10
let num4:Double = 10.1