foo.cc:1:2: error: expected unqualified-id before 'for'
  for(int i=0; i<n; i++)
  ^~~
foo.cc:1:15: error: 'i' does not name a type
  for(int i=0; i<n; i++)
               ^
foo.cc:1:20: error: 'i' does not name a type
  for(int i=0; i<n; i++)
                    ^
foo.cc:3:1: error: expected declaration before '}' token
 }
 ^

自豪的采用HydroJudge(https://github.com/hydro-dev/Hydro)进行评测。