四舍五入到小数点后两位

Question

如何将currentRatio舍入到小数点后两位？

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

Answer 1

使用格式字符串四舍五入到两位小数并将double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"

如果你想四舍五入你的最后一位小数，你可以做这样的事情（感谢 Phoen1xUK）：

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

Answer 2

（Swift 4.2 Xcode 11）简单易用的扩展：-

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

用：-

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

Answer 3

更新到 SWIFT 4 和问题的正确答案

如果你想四舍五入到 2 个小数位，你应该乘以 100 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 4

考虑为此目的使用 NumberFormatter，如果您想打印比率的百分比符号或者如果您有货币和大数字之类的东西，它会提供更大的灵活性。

let amount = 10.000001
let formatter = NumberFormatter()
formatter.numberStyle = .decimal
formatter.maximumFractionDigits = 2
let formattedAmount = formatter.string(from: amount as NSNumber)! 
print(formattedAmount) // 10

Answer 5

如果我们想多次格式化 Double ，我们可以添加到上面的答案中，我们可以使用 Double 的协议扩展，如下所示：

extension Double {
    var dollarString:String {
        return String(format: "$%.2f", self)
    }
}

let a = 45.666

print(a.dollarString) //will print "$45.67"

Answer 6

小数点后特定数字的代码为：

var roundedString = String(format: "%.2f", currentRatio)

这里 %.2f 告诉 swift 将这个数字四舍五入到小数点后两位。

Answer 7

@Rounded ，一个 swift 5.1 属性包装器示例：

struct GameResult {
    @Rounded(rule: NSDecimalNumber.RoundingMode.up,scale: 4)
    var score: Decimal
}

var result = GameResult()
result.score = 3.14159265358979
print(result.score) // 3.1416

Answer 8

只是像我这样的菜鸟的快速跟进答案：

通过使用带有 output的函数，您可以使其他答案变得非常容易实现。 例如

  func twoDecimals(number: Float) -> String{
    return String(format: "%.2f", number)
}

这样，无论何时您想将一个值抓取到 2 个小数位，您只需键入

twoDecimals ('你的号码在这里')

...

简单！

Ps 你也可以让它返回一个浮点值或任何你想要的值，然后在字符串转换后再次转换它，如下所示：

 func twoDecimals(number: Float) -> Float{
    let stringValue = String(format: "%.2f", number)
    return Float(stringValue)!
}

希望有帮助。

Answer 9

String(format: "%.2f", Double(round(1000*34.578)/1000))

输出：34.58

Answer 10

也许还有：

// Specify the decimal place to round to using an enum
public enum RoundingPrecision {
    case ones
    case tenths
    case hundredths
    case thousands
}

extension Double {
    // Round to the specific decimal place
    func customRound(_ rule: FloatingPointRoundingRule, precision: RoundingPrecision = .ones) -> Double {
        switch precision {
        case .ones: return (self * Double(1)).rounded(rule) / 1
        case .tenths: return (self * Double(10)).rounded(rule) / 10
        case .hundredths: return (self * Double(100)).rounded(rule) / 100
        case .thousands: return (self * Double(1000)).rounded(rule) / 1000
        }
    }
}

let value: Double = 98.163846
print(value.customRound(.toNearestOrEven, precision: .ones)) //98.0
print(value.customRound(.toNearestOrEven, precision: .tenths)) //98.2
print(value.customRound(.toNearestOrEven, precision: .hundredths)) //98.16
print(value.customRound(.toNearestOrEven, precision: .thousands)) //98.164

保留小数，不截断而是四舍五入

有关详细信息，请参阅甚至指定的舍入规则

Answer 11

试试这个，你会得到更好的结果而不是 0.0

extension Double {
    func rounded(toPlaces places:Int) -> Double {
        let divisor = pow(10.0, Double(places))
        return (self * divisor).rounded() / divisor
    }
    func toRoundedString(toPlaces places:Int) -> String {
        let amount = self.rounded(toPlaces: places)
        let str_mount = String(amount)
        
        let sub_amountStrings = str_mount.split(separator: ".")
        
        if sub_amountStrings.count == 1
        {
          var re_str = "\(sub_amountStrings[0])."
            for _ in 0..<places
            {
                re_str += "0"
            }
            return re_str
         
        }
        else if sub_amountStrings.count > 1, "\(sub_amountStrings[1])".count < places
        {
            var re_str = "\(sub_amountStrings[0]).\(sub_amountStrings[1])"
            let tem_places = (places -  "\(sub_amountStrings[1])".count)
              for _ in 0..<tem_places
              {
                  re_str += "0"
              }
            return re_str
        }
        
        return str_mount
    }
}

Answer 12

如果你给它 234.545332233 它会给你 234.54

let textData = Double(myTextField.text!)!
let text = String(format: "%.2f", arguments: [textData])
mylabel.text = text

Answer 13

只需一行代码：

 let obj = self.arrayResult[indexPath.row]
 let str = String(format: "%.2f", arguments: [Double((obj.mainWeight)!)!])