no error???? why???

[jpn]

thanks a lot jpn but i cud not understand tht how u got the 3 lines or error u have given in ur reply.
plz explain then how can i know the logaical error like the one i did in my code in slot.

Are you running the program in Visual Studio? It should appear in the debug output window.

and can u tel me the way to draw line n all on central widget and

Override QWidget::paintEvent() for the widget you want to paint on and use QPainter to draw the line. For example, if you want to paint on the central widget in a main window, you must reimplement the paintEvent() for the central widget, not for the main window.

activate context menu(floating menu)

See this post.