so, you want for each row to compute the sum ...

and what do you want to do with it?

I presume you want to put that value into 1 of the colums, aka the last one?

```
foreach (DataRow rows in dt.Rows)
{
int sum_row = 0;
for (int i = 0; i < dt.Columns.Count ; i++)
{
int number = Convert.ToInt32(rows.Field<int>(i));
sum_row += number;
}
rows.Field( dt.Columns) = sum_row;
}
dataGridView1.DataSource = dt;
```