I just updated to Sierra and it seems my compiler fell apart for some reason.
The code I wrote worked fine before the update, so I\'m sure its not an issue there but
There are multiple options:
xcode-select --install
and try compiling. If that fails,gcc -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.11.sdk source.cpp
. This obviously assuming you have SDK installed in that location. Replace with whatever location exist there.