/in/foo.cc: In function 'int main()':
/in/foo.cc:9:10: error: 'i' was not declared in this scope
     for( i=1;i<=n;++i) 
          ^
/in/foo.cc:12:9: error: 'i' was not declared in this scope
     for(i=1;i<=n;++i) if (f[a[i]]) ++ans;
         ^