swiftnsdecimalnumber

How to store 1.66 in NSDecimalNumber

I know float or double are not good for storing decimal number like money and quantity. I'm trying to use NSDecimalNumber instead. Here is my code in Swift playground.

let number:NSDecimalNumber = 1.66
let text:String = String(describing: number)
NSLog(text)

The console output is 1.6599999999999995904

How can I store the exact value of the decimal number 1.66 in a variable?

Solution

  • In 

    let number:NSDecimalNumber = 1.66

    the right-hand side is a floating point number which cannot represent the value "1.66" exactly. One option is to create the decimal number from a string:

    let number = NSDecimalNumber(string: "1.66")
print(number) // 1.66

    Another option is to use arithmetic:

    let number = NSDecimalNumber(value: 166).dividing(by: 100)
print(number) // 1.66

    With Swift 3 you may consider to use the "overlay value type" Decimal instead, e.g. 

    let num = Decimal(166)/Decimal(100)
print(num) // 1.66

    Yet another option:

    let num = Decimal(sign: .plus, exponent: -2, significand: 166)
print(num) // 1.66

    Addendum:

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