/usr/bin/ld: cannot find

When you make the call to gcc it should say

g++ -Wall -I/home/alwin/Development/Calculator/ -L/opt/lib main.cpp -lcalc -o calculator

not -libcalc.so 

I have a similar problem with auto-generated makes.

You can create a soft link from your compile directory to the library directory. Then the library becomes "local".

cd /compile/directory

ln -s  /path/to/libcalc.so libcalc.so

@Alwin Doss You should provide the -L option before -l. You would have done the other way round probably. Try this :)

You need to add -L/opt/lib to tell ld to look there for shared objects.

Add -L/opt/lib to your compiler parameters, this makes the compiler and linker search that path for libcalc.so in that folder.