using System;

public class Test
{
	public static void Main()
	{
		foreach (var test in new[]{ "1", "1.5", "2.125", "3 7/8", "5/16" })
        {
            Console.WriteLine("{0,-5} = {1:0.000}", test, new FractionalNumber(test));
        }
	}
}

    public class FractionalNumber
    {
        public Double Result
        {
            get { return this.result; }
            private set { this.result = value; }
        }
        private Double result;

        public FractionalNumber(String input)
        {
            this.Result = this.Parse(input);
        }

        private Double Parse(String input)
        {
            input = (input ?? String.Empty).Trim();
            if (String.IsNullOrEmpty(input))
            {
                throw new ArgumentNullException("input");
            }

            // standard decimal number (e.g. 1.125)
            if (input.IndexOf('.') != -1 || (input.IndexOf(' ') == -1 && input.IndexOf('/') == -1 && input.IndexOf('\\') == -1))
            {
                Double result;
                if (Double.TryParse(input, out result))
                {
                    return result;
                }
            }

            String[] parts = input.Split(new[] { ' ', '/', '\\' }, StringSplitOptions.RemoveEmptyEntries);

            // stand-off fractional (e.g. 7/8)
            if (input.IndexOf(' ') == -1 && parts.Length == 2)
            {
                Double num, den;
                if (Double.TryParse(parts[0], out num) && Double.TryParse(parts[1], out den))
                {
                    return num / den;
                }
            }

            // Number and fraction (e.g. 2 1/2)
            if (parts.Length == 3)
            {
                Double whole, num, den;
                if (Double.TryParse(parts[0], out whole) && Double.TryParse(parts[1], out num) && Double.TryParse(parts[2], out den))
                {
                    return whole + (num / den);
                }
            }

            // Bogus / unable to parse
            return Double.NaN;
        }

        public override string ToString()
        {
            return this.Result.ToString();
        }

        public static implicit operator Double(FractionalNumber number)
        {
            return number.Result;
        }
    }