Automatic row addition in gridview on button click

Question

I have two textbox, one button and one gridview. i want that when i click on button, two textbox values will be added to gridview's 1st row. then when i again click on the button, two textbox values will be added to the gridview's 2nd row and so on... I am able to add gridview's 1st row by clicking button, but unable to do further. please help me on these by checking below attached code.