小编sar*_*ark的帖子

我编写了一个简单的 swift 程序来显示运行电气设备的成本。该程序运行良好（只是有点笨拙 - 我是 swift 的新手！）但结果显示小数点后有几个数字，所以我试图将其四舍五入到小数点后两位。我运气不太好！我的代码是：

var pricePerkWh: Double = 13.426
var watts: Double = 5.0
var hours: Double = 730.0
var KW: Double = watts/1000
var kWh: Double = KW*hours
var penceMonth: Double = kWh*pricePerkWh
var poundMonth:Double = penceMonth/100
var cost = poundMonth.roundTo(places: 2)


print ("It will cost £\(cost) per month") 

根据我在此处阅读的内容，roundTo(places: 2)已使用，但这导致错误

error: Power Costs.playground:6:12: error: value of type 'Double' has no member 'roundTo'
var cost = poundMonth.roundTo(places: 2)

任何指针将不胜感激！

谢谢