hi how can i delete text (draw text in display with XftDrawString8()) and draw another text in loop in display? Any idea?

If I understand your question correctly, you want to erase some text you've written to a window and write some other text? In that case you'll want to fill that area with the window's background colour, then write your new text.

People with a Windows background tend to equate Xlib with Win32: it isn't even close. Xlib is a low-level drawing library that happens to understand 2 things: windows and events. Windows, in X lingo, are plain canvasses that can receive (and emit) events. They are not widgets/controls/components. In a sense, Xlib is a network-transparent, asynchronous library more akin to GDI. You definitely don't want to use it to write applications or user interfaces. Use a toolkit for that.

Also — and please do not take offense — are you sure you should be attempting X11 programming? It isn't trivial, and your posting history suggests you're barely getting started with GNU/Linux and GCC (and maybe even C). In fact, a lot of your questions are answered in the documentation already, leading me to believe that you aren't even attempting to learn it.