/in/foo.cc: In function 'int main()':
/in/foo.cc:4:11: error: 'cin' was not declared in this scope
     while(cin>>x){
           ^~~
/in/foo.cc:6:8: warning: array subscript has type 'char' [-Wchar-subscripts]
     a[x]++;
        ^
/in/foo.cc:14:2: error: 'cout' was not declared in this scope
  cout<<(char)p<<a[p];
  ^~~~