text: String.IndexOf Method (Char)
  Reports the zero-based index of the first occurrence of the specified Unicode character in this string. how you can search a String for a character using the IndexOf method.
  using System; class Example { static void Main() { // Create a Unicode string with 5 Greek Alpha characters. String szGreekAlpha = new String('\u0391',5); // Create a Unicode string with 3 Greek Omega characters. String szGreekOmega = "\u03A9\u03A9\u03A9"; String szGreekLetters = String.Concat(szGreekOmega, szGreekAlpha, szGreekOmega.Clone()); // Display the entire string. Console.WriteLine("The string: {0}", szGreekLetters); // The first index of Alpha. int ialpha = szGreekLetters.IndexOf('\u0391'); // The first index of Omega. int iomega = szGreekLetters.IndexOf('\u03A9'); Console.WriteLine("First occurrence of the Greek letter Alpha: Index {0}", ialpha); Console.WriteLine("First occurrence of the Greek letter Omega: Index {0}", iomega); } } // The example displays the following output: // The string: OOO?????OOO // First occurrence of the Greek letter Alpha: Index 3 // First occurrence of the Greek letter Omega: Index 0
  Available since 4.5
  .NET Framework
  Available since 1.1
  Portable Class Library
  Supported in: portable .NET platforms
  Silverlight
  Available since 2.0
  Windows Phone Silverlight
  Available since 7.0
  Windows Phone
  Available since 8.1