Which graphic library would you suggest(for statistical graphs)?

[stereoMatching]

I want to draw some statistical graphs by C++,like histogram,line graph, bar graph and so on.
Which library is easy to use, free and efficient?

Thank you very much

[PanGalactic]

libGD. http://www.libgd.org/Main_Page

[stereoMatching]

Thanks a lot. I was considering about openGL, QT4 and the other library, but they are too complicated and too big for me.