title: How to convert char to string in C++?
body: <p>I have a string variable <code>s</code>, and I have a map data structure(with string keys) <code>m</code>.</p>
  
  <p>I want to check if each letter in <code>s</code> is present in <code>m</code>, so I do <code>m.containsKey(s[i])</code>.</p>
  
  <p>Since, map containsKey function expects string argument, I get the following error:</p>
  
  <pre><code>invalid conversion from char to const char* 
  </code></pre>
  
  <p>Any ideas, on how to convert a char to a string data-type?</p>