take_damage_sane.c

void take_damage(
   const Enemy *enemy, 
   int damage) {
   
   assert(enemy != NULL && "enemy must not be NULL!");
   assert(damage > 0 && "damage must be more than 0!");

   enemy->health -= damage;
   if (enemy->health <= 0) {
      // Do whatever a dead enemy should be doing
   }
}