15.x — Chapter 15 summary and quiz

Chapter Review

Inside every member function, the keyword this is a const pointer that holds the address of the current implicit object. We can have functions return *this by reference in order to enable method chaining, where several member functions can be called on the same object in a single expression.

Prefer to put your class definitions in a header file with the same name as the class. Trivial member functions (such as access functions, constructors with empty bodies, etc…) can be defined inside the class definition.

Prefer to define non-trivial member functions in a source file with the same name as the class.

A type that is defined inside a class type is called a nested type (or member type). Type aliases can also be nested.

Member functions defined inside a class template definition can use the template parameters of the class template itself. Member functions defined outside the class template definition must resupply a template parameter declaration, and should be defined (in the same file) just below the the class template definition.

static member variables are static duration members that are shared by all objects of the class. Static members exist even if no objects of the class have been instantiated. Prefer to access them using the class name, the scope resolution operator, and the members name.

Making static members inline allows them to be initialized inside the class definition.

static member functions are member functions that can be called with no object. They do not have a *this pointer, and cannot access non-static data members.

Inside the body of a class, a friend declaration (using the friend keyword) can be used to tell the compiler that some other class or function is now a friend. A friend is a class or function (member or non-member) that has been granted full access to the private and protected members of another class. A friend function is a function (member or non-member) that can access the private and protected members of a class as though it were a member of that class. A friend class is a class that can access the private and protected members of another class.

Quiz time

Question #1

Let’s create a random monster generator. This one should be fun.

a) First, let’s create an scoped enumeration of monster types named MonsterType. Include the following monster types: Dragon, Goblin, Ogre, Orc, Skeleton, Troll, Vampire, and Zombie. Add an additional max_monster_types enum so we can count how many enumerators there are.

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b) Now, let’s create our Monster class. Our Monster will have 4 attributes (member variables): a type (MonsterType), a name (std::string), a roar (std::string) and the number of hit points (int).

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c) enum class MonsterType is specific to Monster, so make MonsterType a nested enum inside Monster and rename it to Type.

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d) Create a constructor that allows you to initialize all of the member variables.

The following program should compile:

int main()
{
	Monster skeleton{ Monster::skeleton, "Bones", "*rattle*", 4 };

	return 0;
}

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e) Now we want to be able to print our monster so we can validate it’s correct. Write two functions: One called getTypeString() that returns the monster’s type as a string, and one called print() that matches the output in the sample program below.

The following program should compile:

int main()
{
	Monster skeleton{ Monster::skeleton, "Bones", "*rattle*", 4 };
	skeleton.print();

	return 0;
}

and print:

Bones the skeleton has 4 hit points and says *rattle*

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f) Now we can create a random monster generator. Let’s consider how our MonsterGenerator will work. Ideally, we’ll ask it to give us a Monster, and it will create a random one for us. Because MonsterGenerator doesn’t have any state, this is a good candidate for a namespace.

Create a MonsterGenerator namespace. Create function within named generate(). This should return a Monster. For now, make it return Monster{ Monster::Type::skeleton, "Bones", "*rattle*", 4};

The following program should compile:

int main()
{
	Monster m{ MonsterGenerator::generate() };
	m.print();

	return 0;
}

and print:

Bones the skeleton has 4 hit points and says *rattle*

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g) Add two more functions to the MonsterGenerator namespace. getName(int) will take a number between 0 and 5 (inclusive) and return a name of your choice. getRoar(int) will also take a number between 0 and 5 (inclusive) and return a roar of your choice. Also update your generate() function to call getName(0) and getRoar(0).

The following program should compile:

int main()
{
	Monster m{ MonsterGenerator::generate() };
	m.print();

	return 0;
}

and print:

Blarg the skeleton has 4 hit points and says *ROAR*

Your name and sound will vary based on what you chose.

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h) Now we’ll randomize our generated monster. Grab the “Random.h” code from 8.20 -- Generating random numbers using Mersenne Twister and save it as Random.h. Then use Random::get() to generate a random monster type, random name, random roar, and random hit points (between 0 and 100).

The following program should compile:

#include "Random.h"

int main()
{
	Monster m{ MonsterGenerator::generate() };
	m.print();

	return 0;
}

and print something like this:

Mort the zombie has 61 hit points and says *growl*

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16.1Introduction to containers and arrays
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