/in/foo.c: In function 'main':
/in/foo.c:6:3: error: 'in' undeclared (first use in this function)
   in"hello, world\n");
   ^~
/in/foo.c:6:3: note: each undeclared identifier is reported only once for each function it appears in
/in/foo.c:6:5: error: expected ')' before string constant
   in"hello, world\n");
     ^~~~~~~~~~~~~~~~