The Builder automatically sets the type of file based on the file's extension. If you need to manually override the Builder's choice:
Note, however, that the compiler will always be selected based on the file's extension, not the file type. So for instance, even if you set the type for foo.c to Fortran, the C compiler will still be used instead of the Fortran compiler. Therefore, you will need to rename the file if you want to use a different compiler.