title: How to check the length of an input? (C++)
body: <p>I have a program that allows the user to enter a level number, and then it plays that level:</p>
  
  <pre><code>char lvlinput[4];
  std::cin.getline(lvlinput, 4)
  char param_str[20] = "levelplayer.exe "
  strcat_s(param_str, 20, lvlinput);
  system(param_str);
  </code></pre>
  
  <p>And the level data is stored in folders \001, \002, \003, etc., etc. However, I have no way of telling whether the user entered three digits, ie: 1, 01, or 001.  And all of the folders are listed as three digit numbers.  I can't just  check the length of the lvlinput string because it's an array, so How could I make sure the user entered three digits?</p>