Welcome to the Lounge

// required
using System.Collections.Generic;

public class OrdinalData : List<OrdinalNumberData>
{
    // removed because the code belongs to a client  
}

// string numberName
// integer number
// string roman numeral
// string ordinal number
// string classifier
// example format: one~1~I~first~1st
public class OrdinalNumberData
{
    public string NumberName { set; get; }
    public int Number { set; get; }
    public string RomanNumeral { set; get; }
    public string OrdinalNumber { set; get; }
    public string Classifier { set; get; }
}

public class IntList : List<decimal>
    {
        public decimal NumericValue
        {
            get
            {
                DoMath(100);
                DoMath(1000);
                DoMath(1000000);
                DoMath(1000000000); 
                DoMath(1000000000000);
                decimal value = 0;
                foreach(decimal item in this)
                {
                    value += item;
                }
                return value;
            }
        }

        private void DoMath(decimal value)
        {
            int index = this.IndexOf(value);
            if (index >= 1)
            {
                value *= this[index-1];
                this[index] = value;
                this[index - 1] = 0;
            }
        }

        public int IndexOf(decimal value)
        {
            int index = -1;
            for (int i = 0; i < this.Count; i++)
            {
                if (this[i] == value)
                {
                    index = i;
                    break;
                }
            }
            return index;
        }
    }

    public static class NumberTranslator
    {
        private static IntList values;
        public static Dictionary<string, decimal> numbers = new Dictionary<string, decimal>()
        {
            {"ZERO", 0},
            {"FIRST", 1},
            {"ONE", 1},
            {"SECOND", 2},
            {"TWO", 2},
            {"THIRD", 3},
            {"THREE", 3},
            {"FOUR", 4},
            {"FIF", 5},
            {"FIVE", 5},
            {"SIX", 6},
            {"SEVEN", 7},
            {"EIGH", 8},
            {"NINE", 9},
            {"TEN", 10},
            {"ELEVEN", 11},
            {"TWELF", 12},
            {"TWELVE", 12},
            {"THIRTEEN", 13},
            {"FOURTEEN", 14},
            {"FIFTEEN", 15},
            {"SIXTEEN", 16},
            {"SEVENTEEN", 17},
            {"EIGHTEEN", 18},
            {"NINETEEN", 19},
            {"TWENTY", 20},
            {"THIRTY", 30},
            {"FOURTY", 40},
            {"FIFTY", 50},
            {"SIXTY", 60},
            {"SEVENTY", 70},
            {"EIGHTY", 80},
            {"NINETY", 90},
            {"HUNDRED", 100},
            {"THOUSAND", 1000},
            {"MILLION", 1000000},
            {"BILLION", 1000000000}
        };

        public static decimal Translate(string text)
        {
            text = text.ToUpper().Trim();
            string trimChars = "TH";
            text = text.Replace("TY", "TY ");
            text = text.Replace("-"," ").Replace("_"," ").Replace("."," ").Replace(",", " ");
            if (text.EndsWith(trimChars))
            {
                text = text.TrimEnd(trimChars.ToArray());
            }
            text = text.Replace("  ", " ");

            values = new IntList();
            string[] parts = text.Split(' ');
            foreach (string numberText in parts)
            {

                if (numbers.Keys.Contains(numberText))
                {
                    values.Add(numbers[numberText]);
                }
                else
                {
                    throw new Exception("Not a number (might be spelled wrong)");
                }
            }
            return values.NumericValue;
        }

decimal value = 0;
value = NumberTranslator.Translate("twelfth");
value = NumberTranslator.Translate("First");
value = NumberTranslator.Translate("One Hundredth");
value = NumberTranslator.Translate("five thousand seven Hundred thirtysecond");

Bergholt Stuttley Johnson wrote:

but the reputation remains