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Chapter 12 FLYAWAY ADVENTURE GAME PLAYING THE GAME _________________________________________________________________ Prior to studying the source code for this game, =============== it would be to your advantage to spend some time FLYAWAY.EXE playing the game to get familiar with what the =============== game does. Load the file FLYAWAY.EXE and begin the adventure through the airport. The executable file is precompiled for you so you can begin executing the program before you have to compile and link the whole thing. The entire program is composed of 12 files and will take a little effort on your part to properly compile and execute it, but that will come later. If you have played adventure games before, sometimes called interactive fiction, you should begin trying various commands to find your way through the airport to your proper plane. If you have not played before, a few hints are in order concerning how to play the game. The object of the game is to get to your proper plane on time so you can fly away to your vacation. Of course there a few obstacles and problems along the way and they will be brought up at the appropriate time, and it will be up to you to solve the puzzles associated with each problem. To add a little excitement, you only have about twenty-five minutes to get to your plane, with each move taking a minute, so you must hurry. Of course, just getting to the plane on time is not enough, there are a few additional requirements. You will find what they are as you progress through the game. You will probably be required to restart the game many times before you arrive at your destination unscathed and on time. THE METHOD OF PLAY _________________________________________________________________ The method of play is extremely simple. You simply wander around the airport looking for things to do and places to go. You move around the airport by giving the system commands to go in a direction with four choices available, north, south, east, or west. You can abbreviate any of these four direction commands to the first letter only, and you can use either upper or lower case. The system may move you to another area of the airport, or it may tell you that you can't go that way. Try loading the game now and typing, the four directions once each to see what happens. If this is not clear, enter the word help to get you started. In addition to moving around, you can pick up items or ask for more information in any of the rooms. Try telling the system to look around the room and see what additional information it gives you Page 12-1 Chapter 12 - Flyaway Adventure Game for each room, some of the clues for solving the puzzle are given in the clues issued in response to a look command. Another important command is inventory which will give you a list of the items you possess at any given point in time. Type the word inventory at this time to see what items you possess. The remainder of the commands consist of two words, a verb and a noun. These can be given in either order, since the system is smart enough to know the difference, and additional words may be given following the legal words. If you give the system a command that is not in its limited vocabulary, it will tell you it doesn't understand that word. Try telling the system to drop an item you possess, or get an item that is located in the room you are currently in. Several friends have played this game with no more knowledge than you have been given. One solved it in 40 minutes, but most took about an hour to complete the game. After you play the game for awhile, return to the text and we will study the source code for the game. The entire source code for the game is on your distribution disk. The game was purposely kept small so the code could be easily grasped by a programming student. There is no reason the game could not have been made much larger by the addition of more rooms, items, and traps. THE FIRST CLASS - clock _________________________________________________________________ Examine the file named CLOCK.HPP for the =============== definition of the clock class. This is the CLOCK.HPP class for the game clock, and only one instance =============== of this class will be used. It will be used for the object time_of_day defined in line 25 of FLYAWAY.CPP. The class is very simple, consisting of only two variables, the hour and the minute, and four methods. The first method is the constructor used to initialize the clock to 8:51 as you can see if you refer to the implementation of this class. The next two methods are used to get the current values of the two variables. The final method is much more interesting since it does much more. It updates the time of day clock and outputs the user prompt to ask for the next command. This may not be the best place to output the user prompt since this class is devoted to the time of day and associated operations, but this was chosen as the place to do it since the time of day is part of the user prompt. You will notice that the clock was initialized to 8:51, but the first time output was 8:52 when you played the game. In order to simplify the coding later, when we need to decide if we made it to the plane on time, the time was incremented at the beginning of each game move. The time is therefore the same when the command is entered and when it is executed, hence the time is incremented prior to even the first output. Page 12-2 Chapter 12 - Flyaway Adventure Game The clock class is by far the simplest class in the adventure game and should be simple for you to understand. After you are sure you understand it, we will go on to the next class. THE SECOND CLASS - items _________________________________________________________________ If you examine the files named ITEMS.HPP and =============== ITEMS.CPP, you will find the complete ITEMS.HPP definitions of the handling of the items that =============== you carried around the airport in the game. There were exactly four transportable items that could be located in each room or carried by yourself, the keys, the candy, the ticket, and the money. The keys and the money keep you from getting through security and the ticket and candy are required to get you safely on the plane and enroute to your destination. The four items are stored in the class named items in the form of TRUE or FALSE since that is the only required indication. A TRUE means the item is located here, and a FALSE means the item is not here. The values of TRUE and FALSE are defined in FLYAWAY.H. Finally, there are six methods to operate on these items. The first method is a constructor to set all items to FALSE, and the next two are used to either get a specific item, or drop one. The fourth method is used to tell us if the item is located here and the last two are used to tell us what items are on hand in this location. You will notice that the final two are different because different text was desired depending on whether you are carrying the item, or it is located in a room somewhere. The #ifndef in line 5 is required because this header file is included in many of the other files and if it is included more than once, there will be a multiple definition, and hence an error. A class only needs to be defined once, so after it is defined by one of the includes, the name ITEMSHPP will be defined and any other defines will be ignored. This is necessary because of the separate compilation capability of C++. This was described in more detail near the end of chapter 7. The #ifndef in the class clock was not required but was included in order to make all class definitions the same. This class is used in line 48 of FLYAWAY.CPP to define an object for the player named personal_items which stores the list of items the player is carrying around. It is also used in the class location as an embedded or nested object to store the items that are located in each of the 19 locations in the game. Page 12-3 Chapter 12 - Flyaway Adventure Game THE FLIGHT AND GATE CLASS - schedule _________________________________________________________________ Examine the files named SCHEDULE.HPP and ================ SCHEDULE.CPP for our first example of a rather SCHEDULE.HPP large class, the one that does the flight and ================ gate scheduling. You will find a large number of variables in this class, and eight methods to handle the variables. Instead of a detailed description of each variable and method, we will only give a brief overview of the class. Only one object of this class is declared named flight_info in line 26 of the program named FLYAWAY.CPP. The constructor initializes the flight possibilities, and the method named shuffle_gates() shuffles all gates around if the player arrives at his correct gate without reading the monitor in the waiting area. Once the monitor in the waiting area is read, the flights_frozen variable is made TRUE. Likewise, the players destination is changed every play by the method named shuffle_flights() until the player reads his ticket invoking the method named list_actual_destination(). This class contains the methods to list the data seen on the monitor, as well as the data seen when invoking the command look at one of the gates. Finally, this class contains the method named check_flight() which searches through the list of requirements to see if the player has completed all requirements to successfully reach the final destination for his vacation. You will notice that several of the location objects were required to be available within this code and are listed as extern in lines 9 through 21 of the implementation of the class. The only other thing to point out is the rest room requirement prior to boarding the flight. Line 23 is where the global variable is defined and initialized, then in line 74 it is set TRUE if the current location is the rest room, since this is called once during each player move. Finally, the state of this variable is checked in line 237 of this file and the appropriate action taken. You will note that the main program is not aware that the rest room variable exists or that anything happens as a result of this variable. In addition to information hiding, we may coin a new term, something like "Information Ignorance", since the main program did not even need to be aware that there was a requirement to visit the rest room. THE MOST USED CLASS - location _________________________________________________________________ The file named LOCATION.HPP is the header file ================ for the class named location. It is the class LOCATION.HPP that controls all of the moves from location to ================ location. Page 12-4 Chapter 12 - Flyaway Adventure Game This class is a bit unusual in that most of the stored data is in the form of pointers to the various entities. The first four are the locations to which we will go if we go in one of the four directions from the current location, moreover they are pointers to those four locations. Next we have pointers to two different character strings associated with this room. Finally in line 24 we declare the object named list_of_items which is an object of class items defined earlier. Note that this is an embedded class, a class embedded within the location class. It is not a parent class which we are inheriting something from. In fact we are instantiating an object of class items for use within the room since the room is allowed to store any combination of the four items contained in the class named items. There is no constructor used with this class since we choose to initialize the locations one by one. Note that a constructor could have been used even though we would have to refer to some items prior to their definition because it is permissible to refer to a pointer to an object before it is declared. The method named init() has 6 variable parameters, all of which are pointers, associated with it which it uses to initialize the first six variables of this object. The last variable, an object of class items, is initialized through use of the constructor associated with its class. Referring to lines 81 through 212 of the main program FLYAWAY.CPP, you will find all of the initialization code for the 19 objects of class location. If you drew a map when you played the game, you will see the interconnections between the various locations embedded in the initialization statements. Notice there is no way to get back to the car from the passenger drop off area, because presumably the car leaves when you get out of it. The next method, named move(), returns a pointer to the new location if a move was legal, otherwise it returns a NULL value. The observant student will also notice that there are special cases involved with getting out of the snack bar and getting through security. These are located here because they are part of the move logic. If you played the game to the complete conclusion, you surely had trouble with at least one of these situations. The rest of the methods in this class should be self explanatory and will not be discussed any further. THE LOCATION MESSAGES _________________________________________________________________ Examine the file named MESSAGE.H for a complete =============== listing of the messages output to the monitor MESSAGE.H when each location was entered. You will also =============== find the text for each of the messages output in response to a look command in this file. These were put into a separate file only for the purpose of reducing the size of the main file. It does not reduce the compile time since Page 12-5 Chapter 12 - Flyaway Adventure Game these messages are not separately compiled. They are included into the file and compiled each time the main file FLYAWAY.CPP is compiled. You will note that a few of the messages have no text at all, only the empty quote marks, but are included in order to have something for the initialization code to work with. THE PROTOTYPES FOR THE STANDARD C CODE _________________________________________________________________ The file named FLYAWAY.H contains the =============== definitions for TRUE and FALSE as well as the FLYAWAY.H enumerated type defining the legal dictionary of =============== words for use in playing the game. The list was started at a value of 1 so the value of zero can be used to indicate that the word in question was not in the library and hence not a legal word for use with the game. Finally, this file contains the prototypes for all of the functions that are used in a normal C fashion rather than being parts of an object. As much of this problem as was felt practical was broken up into objects and the remainder was programmed using standard C functions. You will find that as you develop object oriented techniques, you will not program all of any project with objects but will finally relegate part of it to your old favorite methods. This file, like all other header files, is protected from multiple inclusion by the #ifndef construct discussed earlier. INPUT COMMAND PARSING _________________________________________________________________ The input command parsing routines were not =============== defined as objects but were written as standard COMMAND.CPP C++ code to illustrate that all of a program =============== need not be handled as objects. These routines were written in a separate file to indicate that it is legal and possible to do so in a program that is primarily an object oriented program. The code is straightforward and simple to understand if you study it, so only a few comments will be made about this file. The function get_command() reads two words from the keyboard by calling the function read_a_line() and returns the words if they are a valid verb and noun, otherwise it returns zeros for the two words. There are four functions at the end of this file that are used to determine if a word is a verb, a noun, a direction, or an operation. These are called upon from various places within the program. They should be easy for you to understand. Page 12-6 Chapter 12 - Flyaway Adventure Game THE MAIN PROGRAM _________________________________________________________________ We finally reach the main program, the one that =============== actually does the top level control. Examine FLYAWAY.CPP the program named FLYAWAY.CPP and we will look =============== at some of its interesting characteristics. Beginning with the main() entry point itself, we see that following a call to initialize() and the output of a few lines of text, we are into a single do while loop which terminates when the player enters the word quit or when the verb quit comes up some other way. There are other ways to get the quit because it is generated internally in some cases such as at end of game. The loop itself consists of 6 function or method calls. The first method is called to update the time of day clock and output the players prompt in line 66. Next we call the function get_command() to get the players input command. We perform the required action in line 68 by calling perform_action() which we will describe in a few paragraphs. Finally, we send three messages to the object named flight_info to shuffle the flights and gates and to check if the player has reached one of the gates. Remember that within each of the methods we perform checks to see if we need to do the thing requested in the message and either perform the action or simply return to the caller or message sender. THE WORKING FUNCTION _________________________________________________________________ The only function we have not mentioned yet is the one that does all of the work, the function named perform_action() which begins in line 226. This function simply looks at the verb and noun, if there is one, and causes the correct action to be performed. Because of the way we packaged all of the other routines, this function is a snap to implement and to study. If you go through each of the else clauses in this function, you will have no trouble understanding what action is taken for each of the input commands. You will notice that many of the actions have conditional clauses before the action is taken. For example, it is illegal to buy candy unless the player has money, the location has candy, and the location must be the snack_bar according to the rules of the game. Finally, at the end of this function in line 338, we have the default case if nothing else was attempted. It is assumed that there was something funny requested such as a request to get a monitor. Both of these are legal words but they make no sense together. Page 12-7 Chapter 12 - Flyaway Adventure Game FINAL COMMENTS ON FLYAWAY _________________________________________________________________ Now that you have played the game for awhile and studied the game in detail, you should have an appreciation for how this game can be written. Of course, it could be written in any of several thousand different ways of packaging and definition. This has been only one of the ways. Because the student may be left with the sinking feeling that this method simply fell out of the sky or was arrived at in some other esoteric way, it would only be fair to point out that several earlier attempts at outlining this project were attempted and rejected prior to this arrangement. Object oriented programming requires the same forethought as non-object oriented programming, but the object oriented compiler will help you in the coding and debugging phase since the compiler will find and flag many of the oversight errors we are so good at introducing into our code. It was observed during the coding and debugging phase of this project that in nearly every case, when the program finally got through the compiler, the program would actually run without bombing out the system. This is not always the case using any standard procedural programming language. Page 12-8