title: Calculation in DataGridView column
body: <p>I have a DataGridView in which I want to sum up values from two different columns into a third column.</p>
  
  <p><strong>Example DataGridView:</strong></p>
  
  <pre><code>A   B   Total
  1   2    3
  25  35   60
  5   -5   0
  </code></pre>
  
  <p>I want to add (A+B) in total, just after entering values in <code>A &amp; B column</code> or leaving current row. And also want to set Total Column as <code>ReadOnly</code>.</p>