Help with Damage System

Dear Community



I wanna ask to you how can I make any damage system without using includes?



I mean if there is a possibility to make a different damage system, that a weapon will lower more life or that less life without using external plugins or includes?



Example - I need the sawn-off weapon to make -60 of damage?from the player who receives the shots, is that possible to do without using the above?



If you guys can guide/help me and show me some examples with code please



NOTE: I'm using the callback called OnPlayerTakeDamage(parameters) but i dont have anything of this?