Code is borked

number-to-word-by-gpt.cs

string[] ones = { "one", "two", "three", "four", "five", "six", "seven", "eight", "nine", "ten" };
string[] teens = { "eleven", "twelve", "thirteen", "fourteen", "fifteen", "sixteen", "seventeen", "eighteen", "nineteen" };
string[] tens = { "", "", "twenty", "thirty", "forty", "fifty", "sixty", "seventy", "eighty", "ninety" };
string[] suffixes = { "thousand", "million", "billion", "trillion", "quadrillion", "quintillion", "sextillion" };

string NumberToWords(ulong number)
{
    if (number >= 1 && number <= 10)
    {
        return ones[number - 1];
    }
    else if (number >= 11 && number <= 19)
    {
        return teens[number - 11];
    }
    else if (number >= 20 && number <= 99)
    {
        var remainder = number % 10;
        return $"{tens[number / 10]}{(remainder != 0 ? $"-{ones[remainder - 1]}" : "")}";
    }
    else if (number >= 100 && number <= 999)
    {
	var quotient = (int)Math.Floor((double)(number / 100));
        var remainder = (ulong)Math.Floor((double)(number % 100));
	return $"{ones[quotient - 1]} hundred{(remainder != 0 ? $" and {NumberToWords(remainder)}" : "")}";
    }
    else
    {
        for (var i = suffixes.Length - 1; i >= 0; i--)
        {
            var magnitude = (ulong)Math.Pow(10, 3 * i);
            if (number >= magnitude)
            {
                var quotient = (ulong)Math.Floor((double)number / magnitude);
                var remainder = number % magnitude;
                return $"{NumberToWords(quotient)} {suffixes[i - 1]}{(remainder != 0 ? $" {NumberToWords(remainder)}" : "")}";
            }
        }

        return "zero";
    }
}



while (true)
{
	Console.Write("< ");
	var input = Console.ReadLine();
	try
	{
	    var sanitized = input.Replace("_", "");
	    var words = NumberToWords(ulong.Parse(sanitized));
	    Console.WriteLine("> " + words);
	}
	catch (Exception ex)
	{
	    Console.WriteLine(ex);
	    break;
	}
}

Borked how?

Run it. It's borked.

Recommend writing unit tests at this point^^
1 is ok
10 is ok
100 is not ok, use this: ones[number / 100 - 1], it lacked the -1 there.
151 is ok
1111 is ok
1125 is ok

Also I'm not actually building the whole thing i just use a dib file: https://gist.github.com/Regenhardt/9c3ef2974becd12589287c3cccb530ef

I think I've fixed it. Yeah, this requires tests but too lazy to do that rn.