foo.cc:34:2: error: expected initializer before 'int'
  int i;
  ^~~
foo.cc:35:2: error: expected unqualified-id before 'for'
  for(i=0; i<n; i++)
  ^~~
foo.cc:35:11: error: 'i' does not name a type
  for(i=0; i<n; i++)
           ^
foo.cc:35:16: error: 'i' does not name a type
  for(i=0; i<n; i++)
                ^
foo.cc:38:2: error: expected unqualified-id before 'return'
  return -1;
  ^~~~~~
foo.cc:39:1: error: expected declaration before '}' token
 }
 ^

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