Now that we have our C code written, we'll need to compile it. One of the required flags you must pass to the emcc command is -o <target>, where <target> is the path to the desired output file. The extension of that file will do more than just output that file; it impacts some of the decisions the compiler makes. The following table, taken from Emscripten's emcc documentation at http://kripken.github.io/emscripten-site/docs/tools_reference/emcc.html#emcc-o-target, defines the generated output types based on the file extension specified:

You can disregard the .bc and .o file extensions—we won't need to output LLVM bitcode. The .wasm extension isn't on the emcc Tools Reference page, but it is a valid option if you pass the correct compiler flags. These output options factor into the C/C++ code we write.