You should mention the library on the command line after the object files being compiled: Explanation: the linking is dependent on the order of modules. Symbols are first requested, and then linked in from a library that has them. So you have to specify modules that use libraries first, and libraries after them. Like this: Moreover, in … Read more
Why do you #include lines.cpp in ThreeD.cpp? This is very unusual. Your makefile wants lines.o, so you’re going to compile lines.cpp. Anything defined in lines.cpp will be in lines.o and also in ThreeD.o. There is an intriguing comment in lines.cpp: I think the instructor wants you to break lines.cpp into a .h and a .cpp. … Read more
You should provide output file name after -o option. In your case runexp.o is treated as output file name, not input object file and thus your main function is undefined.