How to induce form to hide rather than dispose upon user [x] button click?

[C# Programming]

I need the window form to hide itself when the user clicks [x] close button in the upper right corner.
Thus it will reside allocated and once user clicks to open it, it will just become visible again.

But upon main program termination it needs to be closed in any case.

[x] button click results in form deal********.

????????