/in/foo.cc: In function 'int num(int, int)':
/in/foo.cc:12:9: warning: 'ret' may be used uninitialized in this function [-Wmaybe-uninitialized]
  return ret;
         ^~~
/in/foo.cc: In function 'int main()':
/in/foo.cc:17:16: warning: 'ret' may be used uninitialized in this function [-Wmaybe-uninitialized]
  cout<<num(n,k);
                ^