Teaching Notes: Module 03

Key Learning Objectives

• Inheritance basics
• Constructor/destructor chaining
• Protected vs private members
• Multiple inheritance and the diamond problem

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Exercise 00: ClapTrap

What It Tests

• Basic class design with OCF
• Using protected for inheritance preparation
• Constructor/destructor messages

Key Values

Attribute	Value
Hit points	10
Energy points	10
Attack damage	0

Common Mistakes

1. Making attributes private instead of protected

   • Derived classes need access

2. Forgetting energy/HP checks

   void ClapTrap::attack(const std::string& target) {
       if (_energyPoints <= 0 || _hitPoints <= 0) {
           std::cout << "ClapTrap " << _name << " can't attack!" << std::endl;
           return;
       }
       _energyPoints--;
       // ...
   }

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Exercise 01: ScavTrap

What It Tests

• Basic inheritance
• Constructor chaining
• Function overriding

Key Values (Different from ClapTrap!)

Attribute	Value
Hit points	100
Energy points	50
Attack damage	20

Common Mistakes

1. Not calling base constructor

   // WRONG
   ScavTrap::ScavTrap(std::string name) {
       _name = name;  // ClapTrap not properly initialized!
   }
   
   // CORRECT
   ScavTrap::ScavTrap(std::string name) : ClapTrap(name) {
       _hitPoints = 100;
       _energyPoints = 50;
       _attackDamage = 20;
   }

2. Wrong construction/destruction order

   • Construction: Base -> Derived
   • Destruction: Derived -> Base

Guiding Questions

• “When you create a ScavTrap, what gets constructed first?”
• “How do you initialize the ClapTrap part of a ScavTrap?”

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Exercise 02: FragTrap

Key Values

Attribute	Value
Hit points	100
Energy points	100
Attack damage	30

Same inheritance pattern as ScavTrap.

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Exercise 03: DiamondTrap

The Diamond Problem

        ClapTrap
        /      \
   ScavTrap  FragTrap
        \      /
       DiamondTrap

Without virtual inheritance, DiamondTrap has TWO ClapTrap subobjects!

Solution: Virtual Inheritance

class ScavTrap : virtual public ClapTrap { };
class FragTrap : virtual public ClapTrap { };
class DiamondTrap : public ScavTrap, public FragTrap { };

Common Mistakes

1. Forgetting virtual keyword

   • Must be on BOTH intermediate classes

2. Not initializing virtual base in most-derived class

   DiamondTrap::DiamondTrap(std::string name)
       : ClapTrap(name + "_clap_name"),  // Virtual base init
         ScavTrap(name),
         FragTrap(name),
         _name(name)
   { }

3. Wrong attribute inheritance

   • HP: FragTrap (100)
   • Energy: ScavTrap (50)
   • Damage: FragTrap (30)
   • attack(): ScavTrap

Guiding Questions

• “What happens if DiamondTrap inherits from both ScavTrap and FragTrap without virtual?”
• “Why does the most-derived class initialize the virtual base?”
• “How do you access the ClapTrap name vs DiamondTrap name?”

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General Tips

Inheritance Visualization

Draw class diagrams showing:

• What each class inherits
• Which members are overridden
• Constructor call order

Testing Construction/Destruction

int main() {
    std::cout << "--- Creating ScavTrap ---" << std::endl;
    ScavTrap s("Scav");
    std::cout << "--- End of main ---" << std::endl;
}
// Should show:
// ClapTrap constructor
// ScavTrap constructor
// ScavTrap destructor
// ClapTrap destructor