C# - How To Calculate Row-wise Sum Of Values In Grid-view And Display It In Grid View

I have a grid view which displays some values. now i have to calculate row wise sum of those values for each row and then display against them.i tried this code but i am getting error as Input String Was not in Correct Format.

public void gv_RowCreated(Object sender, GridViewRowEventArgs e)
{
if (e.Row.RowType == DataControlRowType.DataRow)
{
int total = Convert.ToInt32(e.Row.Cells[1].Text) + Convert.ToInt32(e.Row.Cells[2].Text) + Convert.ToInt32(e.Row.Cells[3].Text) + Convert.ToInt32(e.Row.Cells[4].Text) + Convert.ToInt32(e.Row.Cells[5].Text) + Convert.ToInt32(e.Row.Cells[6].Text) + Convert.ToInt32(e.Row.Cells[7].Text);
((Label)gv.FindControl("Label8")).Text = Convert.ToString(total);
}
}