i've downloaded IUP Version 3.27 on my ubuntu linux so I can work with IUP_FB_EDITOR IDE however the installer of IUP install to /usr/lib64 by default on my system. So you have to create this file: /etc/ld.so.conf.d/IUP.conf with this content:
/usr/lib64
(Adapt it the fit what is on your system)
Save it then run ldconfig.
All of the steps above are run with sudo.
after that IUP_FB_EDITOR IDE runs and works without the need to "sudo ldconfig /usr/lib64" everytime you want to run "./fbnp"