title: Get the index of the nth occurrence of a string?
body: <p>Unless I am missing an obvious built-in method, what is the quickest way to get the <em>n</em>th occurrence of a string within a string?</p>
  
  <p>I realize that I could loop the <a href="https://msdn.microsoft.com/en-us/library/k8b1470s(v=vs.110).aspx" rel="noreferrer">IndexOf</a> method by updating its start index on each iteration of the loop. But doing it this way seems wasteful to me.</p>