四舍五入到小数点后两位

Question

我如何四舍五入电流比率到两个小数位？

let currentRatio = Double (rxCurrentTextField.text!)! / Double (txCurrentTextField.text!)!
railRatioLabelField.text! = "\(currentRatio)"

Answer 1

更新至SWIFT 4，并正确回答问题

如果你想四舍五入到小数点后两位，你应该用100乘，然后四舍五入，然后除以100

var x = 1.5657676754 
var y = (x*100).rounded()/100
print(y)  // 1.57 

Answer 2

（Swift 4.2 Xcode 11）易于使用的扩展：-

extension Double {
    func round(to places: Int) -> Double {
        let divisor = pow(10.0, Double(places))
        return (self * divisor).rounded() / divisor
    }
}

使用：-

if let distanceDb = Double(strDistance) {
   cell.lblDistance.text = "\(distanceDb.round(to:2)) km"
}

Answer 3

使用格式字符串四舍五入到小数点后两位，并将双转换为String：

let currentRatio = Double (rxCurrentTextField.text!)! / Double (txCurrentTextField.text!)!
railRatioLabelField.text! = String(format: "%.2f", currentRatio)

例子：

let myDouble = 3.141
let doubleStr = String(format: "%.2f", myDouble) // "3.14"

如果你想把最后一位小数四舍五入，你可以这样做（谢谢Phoen1xUK）：

let myDouble = 3.141
let doubleStr = String(format: "%.2f", ceil(myDouble*100)/100) // "3.15"