private void dataGridView1_CellEndEdit(object sender, DataGridViewCellEventArgs e)
{
    newvalue = (int)dataGridView1[e.ColumnIndex, e.RowIndex].Value;
}

private void dataGridView1_CellBeginEdit(object sender, DataGridViewCellCancelEventArgs e)
{
    oldvalue = (int)dataGridView1[e.ColumnIndex, e.RowIndex].Value;
}