/in/foo.c: In function 'main':
/in/foo.c:7:3: error: 'cin' undeclared (first use in this function)
   cin>>m>>n;
   ^~~
/in/foo.c:7:3: note: each undeclared identifier is reported only once for each function it appears in
/in/foo.c:17:2: error: 'cout' undeclared (first use in this function)
  cout<<k*l/n;
  ^~~~