/in/foo.c: In function 'main':
/in/foo.c:22:3: error: 'reverse_n' undeclared (first use in this function)
   reverse_n=reverse_n*10+digit;
   ^~~~~~~~~
/in/foo.c:22:3: note: each undeclared identifier is reported only once for each function it appears in
/in/foo.c:18:6: warning: unused variable 'reserse_n' [-Wunused-variable]
  int reserse_n=0;
      ^~~~~~~~~