/in/foo.c: In function 'main':
/in/foo.c:5:10: error: 'i' undeclared (first use in this function)
  int n,a[i];
          ^
/in/foo.c:5:10: note: each undeclared identifier is reported only once for each function it appears in
/in/foo.c:5:8: warning: unused variable 'a' [-Wunused-variable]
  int n,a[i];
        ^