how I can show the sum of in a datagridview column?

int sum = 0;
for (int i = 0; i < dataGridView1.Rows.Count; ++i)
{
    sum += Convert.ToInt32(dataGridView1.Rows[i].Cells[1].Value);
}
label1.Text = sum.ToString();

Fast and clean way using LINQ

int total = dataGridView1.Rows.Cast<DataGridViewRow>()
                .Sum(t => Convert.ToInt32(t.Cells[1].Value));

verified on VS2013