title: Add leading zeroes/0's to existing Excel values to certain length
body: <p>There are many, many questions and quality answers on SO regarding how to prevent leading zeroes from getting stripped when importing to or exporting from Excel.  However, I already have a spreadsheet that has values in it that were truncated as numbers when, in fact, they should have been handled as strings.  I need to clean up the data and add the leading zeros back in.</p>
  
  <p>There is a field that should be four characters with lead zeros padding out the string to four characters.  However:</p>
  
  <pre><code>"23" should be "0023", 
  "245" should be "0245", and
  "3829" should remain "3829"
  </code></pre>
  
  <p>Question: Is there an Excel formula to pad these 0's back onto these values so that they are all four characters?</p>
  
  <p>Note: this is similar to the age old Zip Code problem where New England-area zip codes get their leading zero dropped and you have to add them back in.</p>