title: Add 7 days to SPField.DateTime list field
body: <p>I have a SharePoint list field called ArchiveDate.</p>
  
  <p>In a C# function I'm looping through the list and have the item in question.</p>
  
  <pre class="lang-cs prettyprint-override"><code>foreach (SPListItem fListItem in fList.Items)     
  {      
     foreach (SPField field in fList.Fields)      
      {   
  </code></pre>
  
  <p>If <code>fListItem[field.Id]</code> has that column item with a date in it. How can I add 7 days to that date using C#?</p>
  
  <p>i know I can set the value of the field to today as follows:</p>
  
  <pre><code>         DateTime dt = DateTime.Now; 
           tListItem["Archive Date"] = dt;
           tListItem.Update();   
  </code></pre>