I have used the gcc command on the terminal to compile C programs but all of a sudden, after an update to my Mac\'s OS (to macOS 10.14 Mojave, and XCode 10.0), I started rec
ln -s /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk '/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.15.sdk' might help you. It fixed my problem.