title: Add zero-padding to a string
body: <p>How do I add "0" padding to a string so that my string length is always 4?</p>
  
  <p>Example</p>
  
  <pre><code>If input "1", 3 padding is added = 0001
  If input "25", 2 padding is added = 0025
  If input "301", 1 padding is added = 0301
  If input "4501", 0 padding is added = 4501
  </code></pre>