foo.cc:1:1: error: 'include' does not name a type
    1 | include<iostream>
      | ^~~~~~~
In file included from /usr/include/c++/9/cmath:43,
                 from foo.cc:2:
/usr/include/c++/9/ext/type_traits.h:162:35: error: 'bool __gnu_cxx::__is_null_pointer' redeclared as different kind of entity
  162 |   __is_null_pointer(std::nullptr_t)
      |                                   ^
/usr/include/c++/9/ext/type_traits.h:157:5: note: previous declaration 'template<class _Type> bool __gnu_cxx::__is_null_pointer(_Type)'
  157 |     __is_null_pointer(_Type)
      |     ^~~~~~~~~~~~~~~~~
/usr/include/c++/9/ext/type_traits.h:162:26: error: 'nullptr_t' is not a member of 'std'
  162 |   __is_null_pointer(std::nullptr_t)
      |                          ^~~~~~~~~
foo.cc: In function 'int main()':
foo.cc:11:1: error: 'cin' was not declared in this scope
   11 | cin>>n;
      | ^~~
foo.cc:3:1: note: 'std::cin' is defined in header '<iostream>'; did you forget to '#include <iostream>'?
    2 | #include<cmath>
  +++ |+#include <iostream>
    3 | using namespace std;
foo.cc:18:1: error: 'cout' was not declared in this scope
   18 | cout<<n0<<" - "<<n1<<" = "<<n2<<endl;
      | ^~~~
foo.cc:18:1: note: 'std::cout' is defined in header '<iostream>'; did you forget to '#include <iostream>'?
foo.cc:18:33: error: 'endl' was not declared in this scope
   18 | cout<<n0<<" - "<<n1<<" = "<<n2<<endl;
      |                                 ^~~~
foo.cc:3:1: note: 'std::endl' is defined in header '<ostream>'; did you forget to '#include <ostream>'?
    2 | #include<cmath>
  +++ |+#include <ostream>
    3 | using namespace std;

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