/in/foo.c: In function 'main':
/in/foo.c:12:16: error: 'f' undeclared (first use in this function)
  printf("%d\n",f);
                ^
/in/foo.c:12:16: note: each undeclared identifier is reported only once for each function it appears in
/in/foo.c:5:12: warning: variable 'c' set but not used [-Wunused-but-set-variable]
    int a,b,c,d,e;
            ^