foo.cc: In function 'int main()':
foo.cc:8:8: error: 'a' was not declared in this scope
   cin>>a[i];
        ^
foo.cc:11:6: error: 'a' was not declared in this scope
   if(a[i]==s)
      ^
foo.cc:10:2: warning: this 'for' clause does not guard... [-Wmisleading-indentation]
  for(int i=1;i<=n;i++)
  ^~~
foo.cc:13:3: note: ...this statement, but the latter is misleadingly indented as if it were guarded by the 'for'
   return 0;
   ^~~~~~

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