What are X-WINDOW INCLUDE FILES?

[chioufd@sas.upenn.edu (Fu-Dong Chiou)]

Hi

I tried to compile xcin-2.3, but encounter the following error.

.
.
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checking if `#!' works in shell scripts
checking for gzip to derive installation directory prefix
        chose installation directory prefix 
checking for utmp file.
checking for X-window system.
YOU DO NOT HAVE THE X-WINDOW INCLUDE FILES IN YOUR SYSTEM!!!!
CONFIGURATION TERMINATES!

Can anyone kindly tell me how and where I can put whatever files I need 
to complete the compilation?  Thanks! 

Best wishes,
Chip