string[] column0Array = new string[dataGridView1.Rows.Count];
string[] column1Array = new string[dataGridView1.Rows.Count];

int i = 0;
foreach (DataGridViewRow row in dataGridView1.Rows) {
    column0Array[i] = row.Cells[0].Value != null ? row.Cells[0].Value.ToString() : string.Empty;
    column1Array[i] = row.Cells[1].Value != null ? row.Cells[1].Value.ToString() : string.Empty;
    i++;
}