title: How to find all occurrences of specific string in long text
body: <p>I have some long text (e.g. information about many books) in one string and in one line.</p>
  
  <p>I want to find just ISBN (only number - each number prevents by chars ISBN). I found code how to extract this number on first position. The problem is how to create loop for all text. Can I use it for this example streamreader? Thank you for your answers.</p>
  
  <p><strong>Example:</strong></p>
  
  <pre><code>Sub Main()
      Dim getLiteratura As String = "'Author 1. Name of book 1. ISBN 978-80-251-2025-5.', 'Author 2. Name of Book 2. ISBN 80-01-01346.', 'Author 3. Name of book. ISBN 80-85849-83.'"
      Dim test As Integer = getLiteratura.IndexOf("ISBN")
      Dim getISBN As String = getLiteratura.Substring(test + 5, getLiteratura.IndexOf(".", test + 1) - test - 5)
  
      Console.Write(getISBN)
      Console.ReadKey()
  End Sub
  </code></pre>