how to compare two datagridview values in windows application?

for (int k = 0; k < dataGridView3.Rows.Count; k++)
             {
 for (int i = 0; i < dataGridView1.Rows.Count; i++)
    {

  string j12 = dataGridView3.Rows[k].Cells[1].Value.ToString();

   string J13 = dataGridView3.Rows[k].Cells[2].Value.ToString();
   double m = double.Parse(J13)             if (dataGridView1.Rows[i].Cells[0].Value.ToString() == j12)    
 {

                                                                        dataGridView1.Rows[i].Cells[2].Value = m;
                                                                        dataGridView1.Rows[i].Cells[3].Value = m;
         }
      else
  {
                                                                        dataGridView1.Rows[i].Cells[2].Value = "0.00";
                                                                        dataGridView1.Rows[i].Cells[3].Value = "0.00";

 }
}

Table A
  id   column
  1     data1
  2     data2
  3     data3
  4     data4

Table B
  id   column
  1     data10
  3     data30

Table C
  id    column
  1        0
  2      data2
  3        0
  4      data4