title: Batch - If not defined a variable
body: <p>What can I do if I want to echo a warning if the variable <code>favnum</code> is not filled?</p>
  
  <p>I already tried this:</p>
  
  <pre><code>echo What's your favorite color?
  echo.
  set /p favnum="&gt;"
  
  if not defined favnum(
  goto nope
  )
  </code></pre>