title: Replace multiple pair of characters in string
body: <p>I want to replace all occurrence of 'a' with 'b', and 'c' with 'd'.</p>
  
  <p>My current solution is:</p>
  
  <pre><code>std::replace(str.begin(), str.end(), 'a', 'b');
  std::replace(str.begin(), str.end(), 'c', 'd');
  </code></pre>
  
  <p>Is it possible do it in single function using the std?</p>