title: XOpenDisplay(NULL) fails to connect to X
body: <p>I was given a fairly large program to compile and run with extremely vague instructions on how to properly configure my system and install the program.  I was told to use a Windows, install Cygwin, navigate to the program's base directory, and type "make".  I installed Cygwin on a 64-bit Windows 7 in C:\cygwin64 as the main user (I also installed all of the default packages, plus a few extras) and then ran the makefile included with the program (this worked with no problems).  When trying to run the executable with a required file argument, I was simply given the error message "cannot connect to X server."  Upon examination of the code, it appears that this error was caused by a line setting <code>display=XOpenDisplay(NULL)</code> and then exiting when this resulted in <code>display == NULL</code>.  Earlier, "display" had been declared as a variable of type Display.  Is there any way I can get the program to connect to the X server?  I have been assured that the installation of the program is extremely easy, but I'm not so sure...  Thanks in advance.</p>