private void button1_Click(object sender, EventArgs e)
    {
        dataGridView1.RowCount = Convert.ToInt16(numericUpDown1.Value);
    }

    private void button2_Click(object sender, EventArgs e)
    {
        int n = Convert.ToInt16(numericUpDown1.Value);
        double[] a = new double[n];
        for (int i = 0; i < n; i++)
        {
            a[i] = Convert.ToDouble(dataGridView1.Rows[i].Cells[0].Value);
        }
        double v = a[0];
        for (int i = 0; i < n; i++)
            if (a[i] > 0)
            {
                v = v + a[i];
            }

double v = a[0];
for (int i = 0; i < n; i++)