foo.cc: In function 'int main()':
foo.cc:19:2: error: 'cin' was not declared in this scope
  cin>>a>>b>>c;
  ^~~
foo.cc:19:2: note: suggested alternative: 'main'
  cin>>a>>b>>c;
  ^~~
  main
foo.cc:21:2: error: 'cout' was not declared in this scope
  cout<<a<<'^'<<b<<" mod "<<c<<'='<<d;
  ^~~~

[Hydro](https://hydro.ac)提供评测服务