如何使用NSDecimalNumber？

import Foundation

let decimalNumber1 = NSDecimalNumber(value: 10.5)
let decimalNumber2 = NSDecimalNumber(value: 3.2)

let sum = decimalNumber1.adding(decimalNumber2)
let difference = decimalNumber1.subtracting(decimalNumber2)
let product = decimalNumber1.multiplying(by: decimalNumber2)
let quotient = decimalNumber1.dividing(by: decimalNumber2)

let currencyRate = NSDecimalNumber(value: 6.5)
let amountInUSD = NSDecimalNumber(value: 100)
let amountInCNY = amountInUSD.multiplying(by: currencyRate)

let comparisonResult = decimalNumber1.compare(decimalNumber2)
if comparisonResult == .orderedAscending {
    print("decimalNumber1 is less than decimalNumber2")
} else if comparisonResult == .orderedDescending {
    print("decimalNumber1 is greater than decimalNumber2")
} else {
    print("decimalNumber1 is equal to decimalNumber2")
}