将整数转换为书面数字

这应该可以正常工作：

public static class HumanFriendlyInteger{    static string[] ones = new string[] { "", "One", "Two", "Three", "Four", "Five", "Six", "Seven", "Eight", "Nine" };    static string[] teens = new string[] { "Ten", "Eleven", "Twelve", "Thirteen", "Fourteen", "Fifteen", "Sixteen", "Seventeen", "Eighteen", "Nineteen" };    static string[] tens = new string[] { "Twenty", "Thirty", "Forty", "Fifty", "Sixty", "Seventy", "Eighty", "Ninety" };    static string[] thousandsGroups = { "", " Thousand", " Million", " Billion" };    private static string FriendlyInteger(int n, string leftDigits, int thousands)    {        if (n == 0)        { return leftDigits;        }        string friendlyInt = leftDigits;        if (friendlyInt.Length > 0)        { friendlyInt += " ";        }        if (n < 10)        { friendlyInt += ones[n];        }        else if (n < 20)        { friendlyInt += teens[n - 10];        }        else if (n < 100)        { friendlyInt += FriendlyInteger(n % 10, tens[n / 10 - 2], 0);        }        else if (n < 1000)        { friendlyInt += FriendlyInteger(n % 100, (ones[n / 100] + " Hundred"), 0);        }        else        { friendlyInt += FriendlyInteger(n % 1000, FriendlyInteger(n / 1000, "", thousands+1), 0); if (n % 1000 == 0) {     return friendlyInt; }        }        return friendlyInt + thousandsGroups[thousands];    }    public static string IntegerToWritten(int n)    {        if (n == 0)        { return "Zero";        }        else if (n < 0)        { return "Negative " + IntegerToWritten(-n);        }        return FriendlyInteger(n, "", 0);    }}

（经过编辑以修复带有百万，十亿等错误）