How can I know the label's numbers of line?

I have a problem with my label. I am resizing the font of the label using a slider but i have to maintain the number of lines of my label. for example i have 3 lines of text when i will resize it. it must maintains 3 lines only. but in my code when I resize the font the label's number of lines is not maintaining. Thanks for the help.I have a problem with my label. I am resizing t