11.x — Chapter 11 comprehensive quiz


Inheritance allows us to model an is-a relationship between two objects. The object being inherited from is called the parent class, base class, or superclass. The object doing the inheriting is called the child class, derived class, or subclass.

When a derived class inherits from a base class, the derived class acquires all of the members of the base class.

When a derived class is constructed, the base portion of the class is constructed first, and then the derived portion is constructed. In more detail:

  1. Memory for the derived class is set aside (enough for both the base and derived portions).
  2. The appropriate derived class constructor is called.
  3. The base class object is constructed first using the appropriate base class constructor. If no base class constructor is specified, the default constructor will be used.
  4. The initialization list of the derived class initializes members of the derived class.
  5. The body of the derived class constructor executes.
  6. Control is returned to the caller.

Destruction happens in the opposite order, from most-derived to most-base class.

C++ has 3 access specifiers: public, private, and protected. The protected access specifier allows the class the member belongs to, friends, and derived classes to access the protected member, but not the public.

Classes can inherit from another class publicly, privately, or protectedly. Classes almost always inherit publicly.

Here’s a table of all of the access specifier and inheritance types combinations:

Access specifier in base class Access specifier when inherited publicly Access specifier when inherited privately Access specifier when inherited protectedly
Public Public Private Protected
Private Inaccessible Inaccessible Inaccessible
Protected Protected Private Protected

Derived classes can add new functions, change the way functions that exist in the base class work in the derived class, change an inherited member’s access level, or hide functionality.

Multiple inheritance enables a derived class to inherit members from more than one parent. You should avoid multiple inheritance as much as possible.

Quiz Time

1) For each of the following programs, determine what they output, or if they would not compile, indicate why. This exercise is meant to be done by inspection, so do not compile these (otherwise the answers are trivial).


Show Solution

1b) Hint: Local variables are destroyed in the opposite order of definition.

Show Solution


Show Solution


Show Solution


Show Solution

2a) Write an Apple class and a Banana class that are derived from a common Fruit class. Fruit should have two members: a name, and a color.

The following program should run:

And produce the result:

My apple is red.
My banana is yellow.

Show Solution

2b) Add a new class to the previous program called GrannySmith that inherits from Apple.

The following program should run:

And produce the result:

My apple is red.
My banana is yellow.
My granny smith apple is green.

Show Solution

3) Challenge time! The following quiz question is more difficult and lengthy. We're going to write a simple game where you fight monsters. The goal of the game is to collect as much gold as you can before you die or get to level 20.

Our program is going to consist of 3 classes: A Creature class, a Player class, and a Monster class. Player and Monster both inherit from Creature.

3a) First create the Creature class. Creatures have 5 attributes: A name (std::string), a symbol (a char), an amount of health (int), the amount of damage they do per attack (int), and the amount of gold they are carrying (int). Implement these as class members. Write a full set of getters (a get function for each member). Add three other functions: void reduceHealth(int) reduces the Creature's health by an integer amount. bool isDead() returns true when the Creature's health is 0 or less. void addGold(int) adds gold to the Creature.

The following program should run:

And produce the result:

The orc has 3 health and is carrying 15 gold.

Show Solution

3b) Now we're going to create the Player class. The Player class inherits from Creature. Player has one additional member, the player's level, which starts at 1. The player has a custom name (entered by the user), uses symbol '@', has 10 health, does 1 damage to start, and has no gold. Write a function called levelUp() that increases the player's level and damage by 1. Also write a getter for the level member. Finally, write a function called hasWon() that returns true if the player has reached level 20.

Write a new main() function that asks the user for their name and produces the output as follows:

Enter your name: Alex
Welcome, Alex.
You have 10 health and are carrying 0 gold.

Show Solution

3c) Next up is the Monster class. Monster also inherits from Creature. Monsters have no non-inherited member variables.

First, write an empty Monster class inheriting from Creature, and then add an enum inside the Monster class named Type that contains enumerators for the 3 monsters that we'll have in this game: DRAGON, ORC, and SLIME (you'll also want a MAX_TYPES enumerator, as that will come in handy in a bit).

Show Solution

3d) Each Monster type will have a different name, symbol, starting health, gold, and damage. Here is a table of stats for each monster Type:

Type Name Symbol Health Damage Gold
DRAGON dragon D 20 4 100
ORC orc o 4 2 25
SLIME slime s 1 1 10

Next step is to write a Monster constructor, so we can create monsters. The Monster constructor should take a Type enum as a parameter, and then create a Monster with the appropriate stats for that kind of monster.

There are a number of different ways to implement this (some better, some worse). However in this case, because all of our monster attributes are predefined (not random), we'll use a lookup table. A lookup table is an array that holds all of the predefined attributes. We can use the lookup table to look up the attributes for a given monster as needed.

So how do we implement this lookup table? It's not hard. We just need two things. First, we need an array that contains an element for each monster Type. Each array element will contain a struct that contains all of the predefined attribute values for that Type of Monster.

Step 1: Create a struct type inside Monster named MonsterData. This struct should have a member for each attribute (name, symbol, health, damage, and gold).
Step 2: Declare an array of that struct as a static member of the class named monsterData (declare this like a normal array member, and then add the word static before it).
Step 3: Add the following code outside of the class. This is the definition for our lookup table:

Now we can index this array to lookup any values we need! For example, to get a Dragon's gold, we can access monsterData[DRAGON].gold.

Use this lookup table to implement your constructor:

The following program should compile:

and print:

A orc (o) was created.

Show Solution

3e) Finally, add a static function to Monster named getRandomMonster(). This function should pick a random number between 0 and MAX_TYPES-1 and return a monster (by value) with that Type (you'll need to static_cast the int to a Type to pass it to the Monster constructor).

You can use the following code to pick a random number:

The following main function should run:

The results of this program should be randomized.

Show Solution

3f) We're finally set to write our game logic!

Here are the rules for the game:

  • The player encounters one randomly generated monster at a time.
  • For each monster, the player has two choices: (R)un or (F)ight.
  • If the player decides to Run, they have a 50% chance of escaping.
  • If the player escapes, they move to the next encounter will no ill effects.
  • If the player does not escape, the monster gets a free attack, and the player chooses their next action.
  • If the player chooses to fight, the player attacks first. The monster's health is reduced by the player's damage.
  • If the monster dies, the player takes any gold the monster is carrying. The player also levels up, increasing their level and damage by 1.
  • If the monster does not die, the monster attacks the player back. The player's health is reduced by the monster's damage.
  • The game ends when the player has died (loss) or reached level 20 (win)
  • If the player dies, the game should tell the player what level they were and how much gold they had.
  • If the player wins, the game should tell the player they won, and how much gold they had

Here's a sample game session:

Enter your name: Alex
Welcome, Alex
You have encountered a slime (s).
(R)un or (F)ight: f
You hit the slime for 1 damage.
You killed the slime.
You are now level 2.
You found 10 gold.
You have encountered a dragon (D).
(R)un or (F)ight: r
You failed to flee.
The dragon hit you for 4 damage.
(R)un or (F)ight: r
You successfully fled.
You have encountered a orc (o).
(R)un or (F)ight: f
You hit the orc for 2 damage.
The orc hit you for 2 damage.
(R)un or (F)ight: f
You hit the orc for 2 damage.
The orc hit you for 2 damage.
(R)un or (F)ight: f
You hit the orc for 2 damage.
You are now level 3.
You found 25 gold.
You have encountered a dragon (D).
(R)un or (F)ight: r
You failed to flee.
The dragon hit you for 4 damage.
You died at level 3 and with 35 gold.
Too bad you can't take it with you!

Hint: Create 4 functions:

  1. The main() function should handle game setup (creating the Player) and the main game loop.
  2. fightMonster() handles the fight between the Player and a single Monster, including asking the player what they want to do, handling the run or fight cases.
  3. attackMonster() handles the player attacking the monster, including leveling up.
  4. attackPlayer() handles the monster attacking the player.

Show Solution

12.1 -- Pointers and references to the base class of derived objects
11.7 -- Multiple inheritance

177 comments to 11.x — Chapter 11 comprehensive quiz

  • Faruk

    Hi I made the Monster Combat Game.It was very fun and it took me about 2 day.My code is very different for the solutions mostly because i used a Entity class that is a base class of the Player and the Enemy, and i also added a Game object with a game loop and states(Menu state, Game state and Quit).Any tips and advice.

    Here's the code:












    • Hi Faruk!

      * Initialize your variables with uniform initialization
      * You don't need to specify the array length when you're initializing an array
      * Use @std::rand, @std::srand and @std::time
      * @std::time wants a pointer as it's argument. Pass nullptr.
      * @fraction should be constexpr
      * Use enum class instead of enum
      * entity.cpp:14: No need for a conditional statement. @operator== returns a boolean.
      * Return/Pass class types by (const) reference or pointer
      * entity.cpp:13: Can be done using @std::max

      I didn't look at everything. If there's anything in particular you want feedback to, please point it out and I'll give it another shot.

  • artur

    Oh, I didn't see the hint in the final quiz 😀 I just did it like that:

    • Hi!

      * Initialize your variables with uniform initialization
      * Use @std::rand, @std::srand and @std::time
      * @std::time wants a pointer as it's argument. Pass nullptr.
      * @fraction should be constexpr
      * Line 31-34: const is unnecessary when returning by value
      * Line 58: @name should be a const reference
      * Line 140: Initialize to a 0-value
      * Line 167: Should be else-if
      * Line 156-163 and 187-194: Duplicate code
      * Line 179: You have @hasWon

  • Hello,
    i have a problem with choosing which access specifiers (private Vs protected), in the third question i started out by writing
    the Creature properties as private but then i found inherited class needs access so instead of writing setters functions and
    fully encapsulate them i changed them to protected as they are many ..

    -Is this a good way of thinking (because there are many variables to encapsulate)?
    -How to choose when designing a solution to a long inheritance chain ?

    also for some reason i wrote the static variable as private, is it better have it private or public for this particular program ?
    design of this

    a very minor typo i think the return statement of main()

    • > Is this a good way of thinking
      If the child classes need direct access to the variables or you know that you're never going to need to filter the values the variables can take, mark them as protected. There's nothing wrong with it.

      > How to choose when designing a solution to a long inheritance chain
      Look up software engineering. It's all about planning a project. Including drawing diagrams and what not to make development smoother. This is usually not done for projects with a single developer.

      > is it better have it private or public for this particular program
      It's not being used outside the class. Private is correct.

  • Stefan Gabriel

    I tried to make ex2a more general(if you can call it that) and it gave me errors when it got in main to the declarations. "call of overloaded banana() is ambiguous" and the same for apple. I looked at lecture 8.5 at the quiz problem but I guess it's not the same.Here is the code:

    • You called

      The compiler can't know if you want to call

      You have to remove default arguments from one of them. Same for @Apple.

      • Stefan Gabriel

        Thank you! I think i understand now but does this mean that in c++ you can't have constructors for different combinations of the parameters if they are of the same type?

        • No. You can have different combinations, they just have to be different from each other.

          But if all parameters of both functions had default values, there'd be no way to tell them apart (unless called with at least 1 argument).

          • Stefan Gabriel

            So how do you treat cases where all the parameters in a constructor are of the same type and you what to cover different calling forms with one parameter, two parameters, etc. ?

            • Hoping I understood you correctly now, you want to do something like this

              This isn't supported. C++20 will have designated initialization, which allows specification of the members that one wants to initialize (similar to R or python for example). But only for aggregate initialization, ie. it won't change anything for classes.

              You could add generators for the class that wraps a call to the proper constructor and passes default arguments to the others

              If you don't like that, you'll have to step up a notch. I'm leaving topics covered by learncpp, you'll have to look this up on your own or ask what you don't understand.

              You could also use a char for the selector and pass 'i', 'j' if you like that better.
              Both the first and last parameter will be removed at compile-time, allowing you to select a constructor without affecting the run-time.

              • Stefan Gabriel

                Thank you for the quick response!
                I learned Python first where you could specify the name of any argument and it's value and the rest would be the default ones. Also, order didn't matter. I wanted to make sure I'm not missing any c++ functionality of constructors/functions.

                • > where you could specify the name of any argument and it's value and the rest would be the default ones
                  Yep, that's what designated initializers will do (For construction, at least. Not for functions.)

                  > order didn't matter
                  It does in C++

                  See the "Designated Initializers" section over at cppreference for more information

Leave a Comment

Put all code inside code tags: [code]your code here[/code]