/in/foo.cc: In function 'int main()':
/in/foo.cc:7:1: error: 'cin' was not declared in this scope
    7 | cin >> n >>  op>> m;
      | ^~~
/in/foo.cc:2:1: note: 'std::cin' is defined in header '<iostream>'; did you forget to '#include <iostream>'?
    1 | #include <stdio.h>
  +++ |+#include <iostream>
    2 | using namespace std;
/in/foo.cc:7:14: error: 'op' was not declared in this scope
    7 | cin >> n >>  op>> m;
      |              ^~
/in/foo.cc:11:5: error: 'cout' was not declared in this scope
   11 |     cout << n+m << endl;
      |     ^~~~
/in/foo.cc:11:5: note: 'std::cout' is defined in header '<iostream>'; did you forget to '#include <iostream>'?
/in/foo.cc:11:20: error: 'endl' was not declared in this scope
   11 |     cout << n+m << endl;
      |                    ^~~~
/in/foo.cc:2:1: note: 'std::endl' is defined in header '<ostream>'; did you forget to '#include <ostream>'?
    1 | #include <stdio.h>
  +++ |+#include <ostream>
    2 | using namespace std;
/in/foo.cc:15:1: error: 'cout' was not declared in this scope
   15 | cout << n-m << endl;
      | ^~~~
/in/foo.cc:15:1: note: 'std::cout' is defined in header '<iostream>'; did you forget to '#include <iostream>'?
/in/foo.cc:15:16: error: 'endl' was not declared in this scope
   15 | cout << n-m << endl;
      |                ^~~~
/in/foo.cc:15:16: note: 'std::endl' is defined in header '<ostream>'; did you forget to '#include <ostream>'?
/in/foo.cc:6:6: warning: unused variable 'f' [-Wunused-variable]
    6 | char f;
      |      ^