[Inkscape-devel] GTK+-3.0 acting strangely

Hi everyone, I recently coded my first GTK+ app. I had first precisely followed the instructions shown on the "Compiling GTK+" page. The app successfully compiled and ran too. Then I had to turn off my computer as i had an errand to run. The problem now is that, when I restarted the laptop, I had to re-install the GTK+ library although it was present in the /opt/gtk folder. Again I was successfully able to compile and run the app. However when i closed the interval pkg-config no lobger recognised gtk+-3.0 as an installed library ! It seems somehow the changes I make when I install the library do not make it after I close the terminal. What to do, I cannot install gtk everytime I need to run my code !