foo.cc: In function ‘int main()’:
foo.cc:3:14: error: ‘cout’ is not a member of ‘std’
    3 |         std::cout<<"Hello World!"<<std::endl;
      |              ^~~~
foo.cc:2:1: note: ‘std::cout’ is defined in header ‘<iostream>’; did you forget to ‘#include <iostream>’?
    1 | #include <ostream>
  +++ |+#include <iostream>
    2 | int main(){