如果有時間
可以參考國際網友的寫法

選我最佳解答

以下是另一篇 C# 的寫法
你認為被打槍的一堆 if 的部份
作者是用「查表」的方式處理
可以參考看看

public static string NumberToWords(int number)
{
    if (number == 0)
        return "zero";

    if (number < 0)
        return "minus " + NumberToWords(Math.Abs(number));

    string words = "";

    if ((number / 1000000) > 0)
    {
        words += NumberToWords(number / 1000000) + " million ";
        number %= 1000000;
    }

    if ((number / 1000) > 0)
    {
        words += NumberToWords(number / 1000) + " thousand ";
        number %= 1000;
    }

    if ((number / 100) > 0)
    {
        words += NumberToWords(number / 100) + " hundred ";
        number %= 100;
    }

    if (number > 0)
    {
        if (words != "")
            words += "and ";

        var unitsMap = new[] { "zero", "one", "two", "three", "four", "five", "six", "seven", "eight", "nine", "ten", "eleven", "twelve", "thirteen", "fourteen", "fifteen", "sixteen", "seventeen", "eighteen", "nineteen" };
        var tensMap = new[] { "zero", "ten", "twenty", "thirty", "forty", "fifty", "sixty", "seventy", "eighty", "ninety" };

        if (number < 20)
            words += unitsMap[number];
        else
        {
            words += tensMap[number / 10];
            if ((number % 10) > 0)
                words += "-" + unitsMap[number % 10];
        }
    }

    return words;
}

1. 哪種程式語言?
2. 說好的程式碼呢?

你知道，什麼叫做backcall應用嘛。

Sample
英文基本上就是 3 個 0 一個單位

units = ['', 'Thousand', 'Million', 'Billion']
lessThanTwenty = ['', 'One', ..., 'Nineteen']
tenDigits = ['', 'Ten', ..., 'Ninety']

既然知道 3 個 0 一個單位
那就每次都取 1000 的餘數就好了
再加上單位的部分

while (num > 0) {
    num3 = _Hundred(num%1000)
    if (num3) {
        res.unshift(`${num3} ${units[i]}`);
    }
    num = Math.floor(num/1000);
    i++
}
return res.join(' and ');

把取出來的數放到另一個 function 去處理

const _Hundred =  (num) => {
    if (num < 20) {
        return `${lessThanTwenty[num]}`
    } else if (num < 100) {
        return `${tenDigits[Math.floor(num/10)]} ${_Hundred(num%10)}`
    } else {
        return `${lessThanTwenty[Math.floor(num /100)]} Hundred ${_Hundred(num % 100)}`
    }
}

邏輯大概就這樣

提供一個糙code給你參考
test.htm

<script>
const alias_arr=['Trillion','Billion','Million','Thousand'];
const dig_str_dict={'0':'none','1':'One',  '2':'Two','3':'Three','4':'Four','5':'Five','6':'Six','7':'Seven','8':'Eight','9':'Nine'}; //百位數&個位數
const teen_str_dict={
  '10':'Ten','11':'Eleven','12':'Tweleve','13':'Thirteen','14':'Fourteen','15':'Fifteen','16':'Sixteen','17':'Seventeen','18':'Eighteen','19':'Nineteen'
}; //10~19的特別處理
const ten_str_dict={
  '0':'none','1':'none','2':'Twenty','3':'Thirty','4':'Fourty','5':'Fifty','6':'Sixty','7':'Seventy','8':'Eighty','9':'Ninety'
}; //非10~19的十位數處理

//用正則把'123456'轉成'123,456'的函式
function numToCommaStr(input_num) {
  return num.toString().replace(/(\d)(?=(?:\d{3})+$)/g, "$1,");
}

function numStrToFinanStr(input_str){
  console.log('Input: '+input_str) // 傳入字串
  const tmp_arr=input_str.split(',');
  if(tmp_arr.length<2){
    return strToDesStr(tmp_arr[0],'');
  }else{
    const aliasFlag=(tmp_arr.length==2?3:(tmp_arr.length==3?2:(tmp_arr.length==4?1:0)));
    let outstr='';
    for(let ti=0;ti<tmp_arr.length;ti++){
      const tmpDesStr=strToDesStr(tmp_arr[ti],(aliasFlag+ti<4?alias_arr[aliasFlag+ti]:''));
      outstr+=(ti>0&&(tmpDesStr!=' ')?', ':'')+tmpDesStr;
    }
    return 'Output: ' + outstr +'dollars.';
  }
}

function strToDesStr(input_str,baseStr){
  const tmp_num=parseInt(input_str[0]=='0'?input_str[1]+input_str[2]:input_str);
  const hunNum=Math.floor(tmp_num/100);
  const tenDigNum=Math.floor(tmp_num%100);
  const tenNum=Math.floor(tenDigNum/10);
  const digNum=Math.floor(tenDigNum%10);
  //console.log('tmp_num:'+tmp_num+ ' hunNum:'+hunNum+' tenDigNum:'+tenDigNum+ ' tenNum:'+tenNum+ ' digNum:'+digNum);
  let tmpStr = (hunNum!==0)? dig_str_dict[hunNum.toString(10)] + ' hundred':'';
  if(tenDigNum>19||tenDigNum<10){
    //非10~19在這邊處理
    tmpStr+= (tmpStr!=''?' and ':'')+(tenNum!=0?ten_str_dict[tenNum.toString(10)]+' ':'') + (digNum!=0?dig_str_dict[digNum.toString(10)]:'');
  }else{
    //10~19在這邊處理
    tmpStr+= (tmpStr!=''?' and ':'')+ teen_str_dict[tenDigNum.toString(10)];
  }
  return tmpStr +' '+ baseStr;
}

let num='10000';
console.log(numStrToFinanStr(numToCommaStr(num)));

num='1999999';
console.log(numStrToFinanStr(numToCommaStr(num)));

num='123456789';
console.log(numStrToFinanStr(numToCommaStr(num)));
</script>

糙code大致思路如下:
1.先宣告相關字典變數 dig_str_dict 處理個位數與百位數 , teen_str_dict 處理10~19數字 ,ten_str_dict處理十位數
2.輸入字串加上千分符的部份用正則處理
3.然後把 輸入字串加上千分符 用','分割傳回陣列 tmp_arr
4.最後用 tmp_arr 跑一次廻圈套字典處理完就完成了。
很多地方你會看到有(?:)的結構，每一個(cond?ttt:fff)你可以看作是一個if(cond){ttt}else{fff}，這個三元運算子的用法可以多利用，好處就是程式行數可以縮減，壞處就是易讀性會變差。

===

被人嫌if太多，可以試試用3元運算子(?:)嚇他，例如:

<script>
let cardNo=1;
cardFace=cardNo>2&&cardNo<11?cardNo:(cardNo==11?'J':(cardNo==12?'Q':(cardNo==13?'K':'A')));
/* 上面這行等同於 if(cardNo>2&&cardNo<11){...}else if(cardNo==11){...}else if(cardNo==12){...}else if(cardNo==13){...}else{...} */
console.log(cardFace);
</script>

好像比轉中文大寫金額還嚕嗦？

C# 程式在綫測試

using System;

class Program
{
  static void Main()
  {
    Console.WriteLine( NumberToWord(10000) );

    Console.WriteLine( NumberToWord(1999999) );

    Console.WriteLine( NumberToWord(123456789) );
  }

  static string NumberToWord(int value)
  {
    string[] scaleWords = { "", "throusand", "million", "billion" };

    string result = "";

    for(int x = 0; value != 0; x++, value /= 1000)
    {
      string block = ThreeDigitsToWord(value % 1000);

      if(block.Length > 0) {
        result = block + scaleWords[x] + ((result.Length > 0) ? "," + result : ((x > 0) ? " " : ""));
      }
    }

    return FirstCharToUpper(result + "dollars");
  }

  static string ThreeDigitsToWord(int value)
  {
    string[] under20Words = { "", "one ", "two ", "three ", "four ", "five ", "six ", "seven ", "eight ", "nine ", "ten ", "eleven ", "twelve ", "thirteen ", "fourteen ", "fifteen ", "sixteen ", "seventeen ", "eighteen ", "nineteen " };

    string[] tenthWords = { "", "", "twenty ", "thirty ", "forty ", "fifty ", "sixty ", "seventy ", "eighty ", "ninety " };

    int valDiv100 = value / 100;

    string front = (valDiv100 > 0) ? under20Words[valDiv100] + "hundred " : "";

    int valMod100 = value % 100;

    string back = (valMod100 < 20) ? under20Words[valMod100] : tenthWords[valMod100 / 10] + under20Words[valMod100 % 10];

    return front + (((front.Length * back.Length) > 0) ? "and " : "") + back;
  }

  static string FirstCharToUpper(string input) =>
      char.ToUpper(input[0]) + input.Substring(1);
}

抱歉，我是來亂的XD
use swift

import Foundation

let format = NumberFormatter()
format.numberStyle = .spellOut
format.locale = Locale(identifier: "en")
for value in [10000, 1999999, 123456789] {
    print("input : \(value)")
    
    let number = NSNumber(value: value)
    print("ouput : \(format.string(from: number) ?? "--") dollars")
}