foo.c: In function ‘main’:
foo.c:6:9: error: ‘cin’ undeclared (first use in this function)
    6 |         cin >>n > m;
      |         ^~~
foo.c:6:9: note: each undeclared identifier is reported only once for each function it appears in
foo.c:7:9: error: ‘cout’ undeclared (first use in this function)
    7 |         cout << n+m;
      |         ^~~~