foo.cc: In function 'int main()':
foo.cc:23:2: error: 'cin' was not declared in this scope
  cin>>a>>b>>c;
  ^~~
foo.cc:23:2: note: suggested alternative:
In file included from foo.cc:3:0:
/usr/include/c++/7/iostream:60:18: note:   'std::cin'
   extern istream cin;  /// Linked to standard input
                  ^~~
foo.cc:25:2: error: 'cout' was not declared in this scope
  cout<<a<<'^'<<b<<" mod "<<c<<'='<<d;
  ^~~~
foo.cc:25:2: note: suggested alternative:
In file included from foo.cc:3:0:
/usr/include/c++/7/iostream:61:18: note:   'std::cout'
   extern ostream cout;  /// Linked to standard output
                  ^~~~

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