title: find indexof single character in string c#
body: <p>I am confused with this code.</p>
  
  <pre><code>string str = sample.indexof("a",0);
  </code></pre>
  
  <p>It's working. But below not working.</p>
  
  <pre><code>string str = sample.indexof("\",0);
  </code></pre>