Error while loading shared libraries: libxxx.so.3: cannot open shared object file: No such file or directory

Typically, it will check /lib, /usr/lib as default library folder while running.

But if your program is using library from another folder,
you should specify it use -L option in gcc:
gcc -Wall hello.c -L/usr/local/lib/x86_64-linux-gnu -lhello -o hello

It will load libhello.so in /usr/local/lib/x86_64-linux-gnu folder

But I still get error after running above command.
To fix it:
$ sudo ldconfig /usr/local/lib/x86_64-linux-gnu

Then build again, it can run successfully.