title: snprintf with unknown size of the char[]
body: <p>How one can create a char array with an unspecified size and then pass it to <code>snprint</code> for formatting it?<br>
  For example:  </p>
  
  <pre class="lang-c prettyprint-override"><code>char str[];
  int total = 100;
  int points = 20;
  snprintf(str, sizeof(str), "You have %d points (total: %d)", points, total);
  printf("%s\n",str);
  </code></pre>
  
  <p>This code is going certainly send me an error because first line is wrong.<br>
  All the examples I saw on internet had something like <code>str[100]</code>.<br>
  I am new to C programming and I would appreciate it if you don't down vote this post.<br>
  Thank you</p>