How to modify this code so that I do Task1 in Even number row and do Task2 in Odd number row ?

I have a code below
For Each gridviewrow As GridViewRow In GridView1.Rows Do task 1 Next
I want to modify it such that If it is 1st, 3rd, 5, 7, 9... row, Do Task1 When it is 2, 4,6,8,10... row, Do task 2
How to write the code ? Thanks