尝试将字符串转换为double时出错

Question

我试图在Swift中将String转换为Double值。经过大量的研究后，我相信这将是将我的字符串转换为Double的最佳方法。但现在我收到一个错误，我不知道如何修复。

var purchaseAmount: Double = 200

var cashTendered: Double = 425.45

var changeRequired: Double = 0

var currencyValues = ["100", "50", "20", "10", "5", "2", "1", "0.50", "0.20", "0.10", "0.05"]

import Cocoa

if cashTendered < purchaseAmount {
    println("Not enough cash tendered")
} else {
    changeRequired = cashTendered - purchaseAmount
    for currency in currencyValues {
        var doubleCurrency = (currency as NSString).doubleValue
        var amountOfCurrency = changeRequired / doubleCurrency
        amountOfCurrency = floor(amountOfCurrency)
        changeRequired = changeRequired - (amountOfCurrency * currency)
        changeRequired = round(changeRequired * 100)/100
        println("$\(currency) X \(Int(amountOfCurrency))")
    }
}

这是错误：

我该怎么做才能解决这个问题？

Answer 1

首先初始化String数组，如下所示：

let currencyValues : [String] = ["100", "50", "20", "10", "5", "2", "1", "0.50", "0.20", "0.10", "0.05"]

然而，由于Swift具有重要功能Type Interface，因此不需要类型声明。但是大多数练习在使用数组时定义类型是很好的。

关于将字符串转换为double，您可以使用以下代码：

for currency : String in currencyValues {
   let doubleCurrency = NSNumberFormatter().numberFromString(currency)!.doubleValue
   print(doubleCurrency)
}

Answer 2

发布代码比图像更容易查看，但如果所有其他方法都失败则有NSNumberFormatter。 NSNumberFormatter的其他优点是允许您转换两个方向并获得货币等方面的良好输出。