Compare columns of DataGridView

Question

i am using dataGridView with 4 columns.

like this:

id	name	num	name2
1	aaa	4	ddd
2	bbb	6	null
3	ccc	1	aaa
4	ddd	5
5	eee	2
6		3

i want to compare id and num columns so that respective value must be display in name2 column