Why stop at 1-9 ...
The C # version of the Squeak Smalltalk method does this for all vigintillion numbers:
public static String AsWords(this int aNumber) { var answer = ""; if (aNumber == 0) return "zero"; if (aNumber < 0) { answer = "negative"; aNumber = Math.Abs(aNumber); } var thousands = new[] {"", "thousand", "million", "billion", "trillion", "quadrillion", "quintillion", "sextillion", "septillion","octillion", "nonillion", "decillion", "undecillion", "duodecillion", "tredecillion", "quattuordecillion", "quindecillion", "sexdecillion", "septendecillion", "octodecillion", "novemdecillion", "vigintillion"}; var thousandCount = 0; while (aNumber > 0) { var underOneThousandName = ThreeDigitName(aNumber % 1000); aNumber = aNumber / 1000; if(underOneThousandName != "") { if (answer != "") answer = "," + answer; answer = underOneThousandName + " " + thousands[thousandCount] + answer; } thousandCount += 1; } return answer; } private static string ThreeDigitName(int aNumberLessThanOneThousand) { if (aNumberLessThanOneThousand == 0) return ""; var units = new[] {"one", "two", "three", "four", "five", "six", "seven", "eight", "nine", "ten", "eleven", "twelve", "thirteen", "fourteen", "fifteen", "sixteen", "seventeen", "eightteen", "nineteen"}; var answer = ""; if (aNumberLessThanOneThousand > 99) { answer = units[(aNumberLessThanOneThousand / 100) - 1] + " hundred"; if (aNumberLessThanOneThousand % 100 != 0) answer += " " + ThreeDigitName(aNumberLessThanOneThousand % 100); return answer; } if (aNumberLessThanOneThousand < 20) return units[aNumberLessThanOneThousand -1]; var multiplesOfTen = new[] {"twenty", "thirty", "forty", "fifty", "sixty", "seventy", "eighty", "ninety"}; answer += multiplesOfTen[(aNumberLessThanOneThousand / 10)-2]; if (aNumberLessThanOneThousand % 10 != 0) answer += "-" + units[(aNumberLessThanOneThousand % 10)-1]; return answer; }