數字轉中文大寫（最大單位只能換到萬）

數字大寫.swift

extension String {
    subscript(_ i: Int) -> String {
        let idx1 = index(startIndex, offsetBy: i)
        let idx2 = index(idx1, offsetBy: 1)
        return String(self[idx1..<idx2])
    }
    
    subscript (r: Range<Int>) -> String {
        let start = index(startIndex, offsetBy: r.lowerBound)
        let end = index(startIndex, offsetBy: r.upperBound)
        return String(self[start ..< end])
    }
    
    subscript (r: CountableClosedRange<Int>) -> String {
        let startIndex =  self.index(self.startIndex, offsetBy: r.lowerBound)
        let endIndex = self.index(startIndex, offsetBy: r.upperBound - r.lowerBound)
        return String(self[startIndex...endIndex])
    }
}

let number = "10".reversed()
let symbol = [
"","拾", "佰", "仟", "萬"
]
let chinese = "零壹貳參肆伍陸柒捌玖"
var result = number.map { (char) -> String in
    let index = Int(String(char))
    return chinese[index ?? 0]
}
for i in 1 ..< result.count {
    if result[i] == "零" {
        if result[i-1] == "零" {
            result[i-1] = ""
        }
        
    }else {
        result[i] += symbol[i]
    }
}
var text = result.reversed().joined()
if text.count > 1, text.hasSuffix("零") {
    text.removeLast()
}


print(text)

另一種寫法
原生spell為小寫，需轉大寫

let formatter = NumberFormatter()
formatter.numberStyle = .spellOut
formatter.locale = Locale(identifier: "zh_TW")
let result = formatter.string(from: number)?
    .map { value -> String in
        switch value {
        case "一": return"壹"
        case "二": return"貳"
        case "三": return"參"
        case "四": return"肆"
        case "五": return"伍"
        case "六": return"陸"
        case "七": return"柒"
        case "八": return"捌"
        case "九": return"玖"
        case "十": return"拾"
        case "百": return"佰"
        case "千": return"仟"
        default: return "\(value)"
        }
    }.joined()