/in/foo.c: In function 'main':
/in/foo.c:48:9: error: 'nn' undeclared (first use in this function)
         nn*=i;
         ^~
/in/foo.c:48:9: note: each undeclared identifier is reported only once for each function it appears in
/in/foo.c:44:10: warning: variable 'u' set but not used [-Wunused-but-set-variable]
     char u;
          ^