/in/foo.c: In function 'main':
/in/foo.c:5:5: error: 'cout' undeclared (first use in this function)
     cout<<"Hello World!"<<endl;
     ^~~~
/in/foo.c:5:5: note: each undeclared identifier is reported only once for each function it appears in
/in/foo.c:5:27: error: 'endl' undeclared (first use in this function)
     cout<<"Hello World!"<<endl;
                           ^~~~