how can add new row using dropdown list value in gridview

I have web page in this this page i use gridview and in this gridview i have textbox. Now i want to add new row using dropdown list value.and this dropdownlist out side the gridview.

like i wnat to add 2 row in grideview i select value from dropdownlist of list box is 2 and add 2 rows in gridview please give me suggest or give me code for this.