what book will you suggest me to read if i want to learn gui using c language.?

Depends. What operating system? For MS-Windows, do you want to use pure win32 api functions? If yes, here is a tutorial. But there are a lot easier ways to write gui programs nowdays. Two of them is CLR/C++ Windows Forms, and C# instead of C.

If you are thinking *nix, then look into low-level X11R6 (there are lots of books on that) or Motief. Again, C++ gives you more and easier options, sich as wxWidgets.

thank you.
i have linux red hat in office.

You could start here -- be prepared for a very long learning curve.

actually i have only one month time for completing my job.
i am developing gui which basically should generate graphs.

so let's see how good i can learn from this tutorials..
and thank you for your help.