using System;

using System.Text.RegularExpressions;

using RegexMatchValues;

​

var text = "Use 3.14 for pi.";

if (Regex.Match(text, @"(\d+)/(\d+)").TryGet(out (int Numerator, int Denominator) fraction))

    Console.WriteLine((double) fraction.Numerator / fraction.Denominator);

else

    Console.WriteLine("No fraction found.");

​