title: Digits in std::string
body: <p>Can you please help me find digits in string without using functions like isdigit? I can only use for loop and pointers. If I have </p>
  
  <pre><code>std::string s {"A year has 365 days"}
  </code></pre>
  
  <p>Why can't I do something like this:</p>
  
  <pre><code>for (int i=0; i&lt;s.size(); i++){
      while (s[i]&gt;='0' &amp;&amp; s[i]&lt;='9) v[i].push_back(s[i]);
  }
  </code></pre>
  
  <p>I know this would store digits 3 6 and 5 in vector and not number 365. But I don't understand why my while loop doesn't work. </p>