/in/foo.cc:3:6: warning: ISO C++ forbids declaration of 'main' with no type [-Wreturn-type]
 main()
      ^
/in/foo.cc: In function 'int main()':
/in/foo.cc:6:2: error: 'cin' was not declared in this scope
  cin>>a>>b;
  ^~~
/in/foo.cc:7:2: error: 'cout' was not declared in this scope
  cout<<a+b;
  ^~~~