/in/foo.c: In function 'main':
/in/foo.c:6:6: error: 'i' undeclared (first use in this function)
  for(i=0;i<100;i++)
      ^
/in/foo.c:6:6: note: each undeclared identifier is reported only once for each function it appears in
/in/foo.c:4:8: warning: variable 'a' set but not used [-Wunused-but-set-variable]
  int n,a[100],x;
        ^