Convert words (string) to Int

Did this for fun... there's probably many edge cases that would fail...

private static Dictionary<string,long> numberTable=
    new Dictionary<string,long>
        {{"zero",0},{"one",1},{"two",2},{"three",3},{"four",4},
        {"five",5},{"six",6},{"seven",7},{"eight",8},{"nine",9},
        {"ten",10},{"eleven",11},{"twelve",12},{"thirteen",13},
        {"fourteen",14},{"fifteen",15},{"sixteen",16},
        {"seventeen",17},{"eighteen",18},{"nineteen",19},{"twenty",20},
        {"thirty",30},{"forty",40},{"fifty",50},{"sixty",60},
        {"seventy",70},{"eighty",80},{"ninety",90},{"hundred",100},
        {"thousand",1000},{"million",1000000},{"billion",1000000000},
        {"trillion",1000000000000},{"quadrillion",1000000000000000},
        {"quintillion",1000000000000000000}};
public static long ToLong(string numberString)
{
    var numbers = Regex.Matches(numberString, @"\w+").Cast<Match>()
         .Select(m => m.Value.ToLowerInvariant())
         .Where(v => numberTable.ContainsKey(v))
         .Select(v => numberTable[v]);
    long acc = 0,total = 0L;
    foreach(var n in numbers)
    {
        if(n >= 1000)
        {
            total += (acc * n);
            acc = 0;
        }
        else if(n >= 100){
            acc *= n;
        }
        else acc += n;          
    }
    return (total + acc)  * ( numberString.StartsWith("minus",
          StringComparison.InvariantCultureIgnoreCase) ? -1 : 1);
}

Here's a method that does that. If you need a wider range, it's easily extensible; just use a long, a ulong, or even a BigInt, and add more items to the modifiers dictionary.

static int ParseEnglish(string number) {
    string[] words = number.ToLower().Split(new char[] {' ', '-', ','}, StringSplitOptions.RemoveEmptyEntries);
    string[] ones = {"one", "two", "three", "four", "five", "six", "seven", "eight", "nine"};
    string[] teens = {"eleven", "twelve", "thirteen", "fourteen", "fifteen", "sixteen", "seventeen", "eighteen", "nineteen"};
    string[] tens = {"ten", "twenty", "thirty", "forty", "fifty", "sixty", "seventy", "eighty", "ninety"};
    Dictionary<string, int> modifiers = new Dictionary<string, int>() {
        {"billion", 1000000000},
        {"million", 1000000},
        {"thousand", 1000},
        {"hundred", 100}
    };

    if(number == "eleventy billion")
        return int.MaxValue; // 110,000,000,000 is out of range for an int!

    int result = 0;
    int currentResult = 0;
    int lastModifier = 1;

    foreach(string word in words) {
        if(modifiers.ContainsKey(word)) {
            lastModifier *= modifiers[word];
        } else {
            int n;

            if(lastModifier > 1) {
                result += currentResult * lastModifier;
                lastModifier = 1;
                currentResult = 0;
            }

            if((n = Array.IndexOf(ones, word) + 1) > 0) {
                currentResult += n;
            } else if((n = Array.IndexOf(teens, word) + 1) > 0) {
                currentResult += n + 10;
            } else if((n = Array.IndexOf(tens, word) + 1) > 0) {
                currentResult += n * 10;
            } else if(word != "and") {
                throw new ApplicationException("Unrecognized word: " + word);
            }
        }
    }

    return result + currentResult * lastModifier;
}