title: FormatException calculating the sum of a column in a ListView
body: <p>I have a problem in my <code>listview</code> that I can't calculate the summation of a specific column.</p>
  
  <p>In my project, I am reading an bit of information from an excel-file to the <code>ListView</code>, then processing this information by doing some of the operations.</p>
  
  <p>Now when I am reading the information to the <code>ListView</code> I can't calculate the summation of a specific column, the function is:-</p>
  
  <pre><code>private void button12_Click(object sender, EventArgs e)
  {
  
      int iSum = 0;
      foreach (ListViewItem o in this.lsvMain.Items )
      {
          iSum = iSum + Convert.ToInt16(o.SubItems[8].Text);
          textBox1.Text = iSum.ToString();
      }
  </code></pre>
  
  <p>The error message appears: <strong>FormatException was unhandled (input string was not in the correct format).</strong> it's indicating to the (iSum..) line.</p>
  
  <p>There isn't any string all the information are integer!</p>