A few comments:
1. Given it's C++ problem, try using C++ containers (instead of array) e.g. vector/list/map.
2. You don't really need to force use of a design. Not yet at least.
3. Comment on the design: Class Data should not be responsible for insertion/deletion/.. Look at it purely from english pov, Data itself shouldn't have this functionality. If you look at your problem stmt, you'll see that you're missing a major class (named Database). Database should be the one who has this functionality.