title: Convert text columns to numbers for large files
body: <p>I have a large Excel sheet auto generated from C#, which outputs all columns as text (this cannot be changed for technical reasons).  I am having trouble writing a macro which will convert the numeric columns to numbers, and do it fast (the sheet contains 80 columns and 20,000 rows).</p>
  
  <p>I have tried iterating over all cells and calling </p>
  
  <pre><code>If IsNumeric(cell.Value) Then cell.Value = CDec(cell.Value)
  </code></pre>
  
  <p>This is very slow AND has the additional problem that I have a special case where strings starting with things such as "0xxx" need to be kept as a string. If I used <code>IsNumeric</code> and then convert to <code>CDec</code>, I LOSE the leading 0!</p>
  
  <p>Is there some simple trick to say detect if one value in a column is a string, then do NOT process the column, else convert them to numeric EXCEPT for the case where we have a leading 0?</p>