CS202 Lab 7 - Code Processing


You and your friends Rad and Banjolina decide to go into business providing web and cell phone support for reward programs like mycokerewards (or, more precisely, like mycokerewards used to be. The current lab is more like Pampers rewards. Mycokerewards got out of the game of redeeming for points, and instead went into sweepstakes. Such is life.) Users can set up accounts with you that will maintain points. Users can accumulate points by collecting codes from various products (such as bottlecaps and 12-packs, as in mycokerewards, or such as diapers and wipes in Pampers rewards), and then they can spend the points on various prizes.

Users can enter codes via a web site, or they can register one or more cell phones with their account, and then they can text codes from a given phone number, which will register the points.

Rad is handling the business and marketing end of this endeavor, and Banjolina is doing all of the web programming. Your job is to write the server that maintains information about users, prizes and codes, and talks with Banjolina's web front-end. Since you haven't taken CS360 yet, your server won't do any real networking. Instead, it will communicate via files and standard input.

As with many of our labs, I give you a header file that defines a class, and you have to implement the methods. I have a driver program that you compile with your code, and that will be the final product.

Here's the header, in include/code_processor.hpp. Unlike the previous labs, there is no commenting here. I have explanations below.

#include <set>
#include <map>
#include <string>

class User {
  public:
     std::string username;
     std::string realname;
     int points;
     std::set <std::string> phone_numbers;
};

class Prize {
  public:
     std::string id;
     std::string description;
     int points;
     int quantity;
};

class Code_Processor {
  public:
    bool New_Prize(const std::string &id, const std::string &description, int points, int quantity);
    bool New_User(const std::string &username, const std::string &realname, int starting_points);
    bool Delete_User(const std::string &username);

    bool Add_Phone(const std::string &username, const std::string &phone);
    bool Remove_Phone(const std::string &username, const std::string &phone);
    std::string Show_Phones(const std::string &username) const;

    int Enter_Code(const std::string &username, const std::string &code);
    int Text_Code(const std::string &phone, const std::string &code);
    bool Mark_Code_Used(const std::string &code);

    int Balance(const std::string &username) const;
    bool Redeem_Prize(const std::string &username, const std::string &prize);
   
    ~Code_Processor();
    bool Write(const std::string &filename) const;

    void Double_Check_Internals() const;   /* You don't write this */

  protected:
    std::map <std::string, User *> Names;
    std::map <std::string, User *> Phones;
    std::set <std::string> Codes;
    std::map <std::string, Prize *> Prizes;
};

While this looks like a mouthful, it's really not that bad. Users store the following data:

Prizes store the following data:

A Code_Processor keeps track of Users, Codes and Prizes. Users are stored in the map Names, which is keyed on their usernames. Phone numbers are stored in the map Phones, which is keyed on the phone numbers, and whose second field points to the user that has registered the cell phone.

There is a set Codes, which stores the codes that have been entered by all users. This set exists so that users can't enter a code more than once. Finally, there is a map Prizes, keyed on the id of each prize.

You'll note that both Names and Phones point to users. In other words, each user has just one User instance, and that is pointed to both in Names and in Phones. If the user has multiple phones, then there will be multiple entries in Phones that point to that user. Moreover, there are two data structures that hold phones -- Phones, which is keyed on the phone number, and the set phone_numbers which is part of the User's data.

Now, you are to write the following methods (I'm omitting the const declarations here, to keep the writeup uncluttered. Obviously, you can see the const declarations in the header):


src/cp_tester.cpp

The program src/cp_tester.cpp is a front end for src/code_processor.cpp. You call it with filenames on the command line argument, and it reads files that have commands to execute on a Code_Processor. If a filename is "-", it reads the commands from standard input. The commands are specified on separate lines -- blank lines are ok, and lines that begin with a pound sign are ignored. Lines may not have more than 20 words on them.

Otherwise, the following commands are supported:

  • "PRIZE id points quantity description": Calls New_Prize() with the given arguments. Id is a single word. Description may be multiple words.

  • "ADD_USER username starting_points realname": Calls New_User() with the given arguments. Username must be one word. Realname can contain any number of words.

  • "DELETE_USER username": Calls Delete_User with the given username.

  • "ADD_PHONE username phone-number": Makes the appropriate Add_Phone() call. Both username and phone-number must be one word.

  • "REMOVE_PHONE username phone-number": Makes the appropriate Remove_Phone() call.

  • "SHOW_PHONES username": Makes the appropriate Show_Phones() call.

  • "ENTER_CODE username code": Makes the appropriate Enter_Code() call. The code should be one word.

  • "TEXT_CODE phone code": Makes the appropriate Text_Code() call.

  • "MARK_USED code ...": You can specify up to 19 codes on a line. It will call Mark_Code_Used() on each of these codes.

  • "BALANCE username": calls Balance() and prints the output.

  • "REDEEM username prize": calls Redeem().

  • "DOUBLE_CHECK": calls Double_Check_Internals().

  • "WRITE filename": calls Write() on the given filename. Explanation below.

  • "QUIT": stops reading. You can simply end input too, and that will stop reading.

    Write()

    The Write() method is very important. Whenever you write a server like this one, you should make it fault-tolerant. In other words, you should make it so that it can save its state so that you can terminate the server and start it up again later. The Write() method should save the Code_Processor's state to the given file and return true. It should return false if it can't open/create the file.

    The format of Write() should be as a file that cp_tester can use as input to recreate the state of the Code_Processor. It should only consist of ADD_USER, PRIZE, ADD_PHONE and MARK_USED lines, and when cp_tester is run with the file as input, it should recreate the state of the Code_Processor.

    I don't care about the order or format of the lines, as long as they create the proper Code_Processor when they are fed to cp_tester. My grading program will test your files by using them as input to my cp_tester and looking at the output of my Write() call.


    Some examples

    Let's start with a very simple example:
    UNIX> bin/cp_tester -
    CP_Tester> ADD_USER tigerwoods 0 Tiger Woods
    ADD_USER successful
    CP_Tester> ADD_USER the-donald 100 Donald Trump
    ADD_USER successful
    CP_Tester> PRIZE mp3 40 5000 Free MP3 download from Bapster
    PRIZE successful
    CP_Tester> PRIZE cancun 10000 1 All expense-paid vacation to Cancun
    PRIZE successful
    CP_Tester> WRITE cp1.txt
    WRITE successful
    CP_Tester> QUIT
    UNIX> cat cp1.txt
    PRIZE     cancun     10000      1 All expense-paid vacation to Cancun
    PRIZE     mp3           40   5000 Free MP3 download from Bapster
    ADD_USER  the-donald   100 Donald Trump
    ADD_USER  tigerwoods     0 Tiger Woods
    UNIX> 
    
    I've added two prizes and two users, and then written the server's state to cp1.txt. You'll note that the order of cp1.txt is different from my input. That's fine -- if you use it as input to cp_tester, it will create the same server state. For example:
    UNIX> bin/cp_tester cp1.txt -
    CP_Tester> BALANCE tigerwoods
    0 Points
    CP_Tester> BALANCE the-donald
    100 Points
    CP_Tester> WRITE cp2.txt
    WRITE successful
    CP_Tester> QUIT
    UNIX> cat cp2.txt
    PRIZE     cancun     10000      1 All expense-paid vacation to Cancun
    PRIZE     mp3           40   5000 Free MP3 download from Bapster
    ADD_USER  the-donald   100 Donald Trump
    ADD_USER  tigerwoods     0 Tiger Woods
    UNIX> 
    
    When I called cp_tester, I gave it two command line arguments: cp1.txt and -. So, it first read commands from cp1.txt, which recreated the same state as when I created cp1.txt, and then it read from standard input. When I entered WRITE cp2.txt, it created cp2.txt, which is identical to cp1.txt, since they have the same state.

    Suppose I call cp_tester with cp1.txt and cp2.txt on the command line. I should expect four error messages, since the users and prizes already exist when it tries to process cp2.txt:

    UNIX> bin/cp_tester cp1.txt cp2.txt
    Prize cancun couldn't be added
    Prize mp3 couldn't be added
    ADD_USER the-donald unsuccessful
    ADD_USER tigerwoods unsuccessful
    UNIX> 
    
    This is because cp_tester checks the return values of the New_Prize() and New_User() calls.

    Let's add a few phone numbers and enter some codes. If you check the hashes using djbhash.cpp from the hashing lecture notes, you'll see that they are each divisible by 13 and not by 17, so they are each worth three points:

    UNIX> /home/jplank/cs202/Notes/Hashing/bin/djbhash | awk '{ print $1%17, $1%13 }'
    Df18ly81CO1mo4
    11 0
    IDWNZJ20ENkAxP
    2 0
    h0yuKnVD6DvRUu
    11 0
    UNIX> bin/cp_tester cp1.txt -
    CP_Tester> ADD_PHONE tigerwoods 865-974-4400       
    ADD_PHONE successful
    CP_Tester> ADD_PHONE tigerwoods 1-800-Big-Putt
    ADD_PHONE successful
    CP_Tester> SHOW_PHONES tigerwoods
    1-800-Big-Putt
    865-974-4400
    CP_Tester> ENTER_CODE tigerwoods Df18ly81CO1mo4
    ENTER_CODE: Added 3 points to tigerwoods.
    CP_Tester> TEXT_CODE 865-974-4400 IDWNZJ20ENkAxP
    TEXT_CODE: Added 3 points.
    CP_Tester> TEXT_CODE 1-800-Big-Putt h0yuKnVD6DvRUu
    TEXT_CODE: Added 3 points.
    CP_Tester> BALANCE tigerwoods
    9 Points
    CP_Tester> WRITE cp3.txt
    WRITE successful
    CP_Tester> QUIT
    UNIX> 
    
    Each ENTER_CODE and TEXT_CODE call adds three points to tigerwoods' account, giving him 9 points in all. After the WRITE call, cp3.txt looks as follows:

    PRIZE     cancun     10000      1 All expense-paid vacation to Cancun
    PRIZE     mp3           40   5000 Free MP3 download from Bapster
    ADD_USER  the-donald   100 Donald Trump
    ADD_USER  tigerwoods     9 Tiger Woods
    ADD_PHONE tigerwoods 1-800-Big-Putt
    ADD_PHONE tigerwoods 865-974-4400
    MARK_USED Df18ly81CO1mo4 IDWNZJ20ENkAxP h0yuKnVD6DvRUu
    

    The phones have been registered to tigerwoods, his point total has been updated, and the codes have been marked as used. Although I put multiple codes on a MARK_USED line, you don't have to. Just remember the 20-word limit on a line.

    And again, your output does not have to match mine -- it simply needs to create the same Code_Processor.

    Let's take a look at an example where some prizes are redeemed:

    UNIX> bin/cp_tester cp3.txt -
    CP_Tester> ADD_USER billgates 500000 Bill Gates
    ADD_USER successful
    CP_Tester> REDEEM tigerwoods mp3
    REDEEM:       either the user doesn't exist,
                  or the prize doesn't exist,
                  or the user can't afford the prize.
    CP_Tester> REDEEM the-donald mp3
    REDEEM successful
    CP_Tester> REDEEM billgates cancun
    REDEEM successful
    CP_Tester> WRITE cp4.txt
    WRITE successful
    CP_Tester> QUIT
    UNIX> cat cp4.txt
    PRIZE     mp3           40   4999 Free MP3 download from Bapster
    ADD_USER  billgates  490000 Bill Gates
    ADD_USER  the-donald    60 Donald Trump
    ADD_USER  tigerwoods     9 Tiger Woods
    ADD_PHONE tigerwoods 1-800-Big-Putt
    ADD_PHONE tigerwoods 865-974-4400
    MARK_USED Df18ly81CO1mo4 IDWNZJ20ENkAxP h0yuKnVD6DvRUu
    UNIX> 
    
    Since tigerwoods only has 9 points, he can't even afford an MP3 from Bapster. the-donald has no such problem, and billgates can easily afford the Cancun vacation (like he needs it). The updated points for the users and the updated quantities for the prizes have been reflected in the file. Since the quantity of cancun went to zero, it has been removed from the system.

    random_codes.cpp

    The program src/random_codes.cpp generates random, valid codes.

    Strategy

    Your strategy here should be to first create a src/code_processor.cpp that implements dummy methods for each method. That way you can compile the program and create a bin/cp_tester. It won't work (except for QUIT), but now you can start programming incrementally.

    The first thing you should do is implement New_Prize(), and then implement the part of the Write() method that creates the file and stores the prizes. Test this by only making PRIZE and WRITE calls in cp_tester.

    Then move onto the others. I implemented these in the following order:

    Although this is a large lab writeup, each of these methods is relatively small. While the grading will of course include the gradescript, the TA's will double-check your destructor by hand.

    The Gradescript

    The gradescript for this program is a little involved, so let me tell you what it does, so that you can navigate it more easily: So, let's examine gradescript 50. There are two files in the gradescript directory that start with 050:
    UNIX> ls /home/jplank/cs202/Labs/Lab7/Gradescript-Examples/050-*.txt
    /home/jplank/cs202/Labs/Lab7/Gradescript-Examples/050-A.txt
    /home/jplank/cs202/Labs/Lab7/Gradescript-Examples/050-B.txt
    UNIX
    
    Let's look at the first -- as you can see, it adds prizes, users and phones, and it sets a bunch of codes as marked:
    UNIX> cat /home/jplank/cs202/Labs/Lab7/Gradescript-Examples/050-A.txt
    PRIZE     cancun     10000      1 All Expense-Paid trip to Cancun
    PRIZE     dogo         570      3 Club Dogo 12-Month Subscription
    PRIZE     habitat       35    100 Donation to Habitat for Humanity
    PRIZE     silver      1100      2 Two DMC Theatres Silver Experience movie tickets
    PRIZE     spinner      750      4 Multi-Function Salad Spinner and Chopper
    ADD_USER  ACamelb30  45158 Arianna Camelback
    ADD_PHONE ACamelb30  590-448-0257
    ADD_PHONE ACamelb30  596-598-2816
    ADD_PHONE ACamelb30  702-497-7232
    ADD_USER  AChurn40   21934 Audrey Churn
    ADD_PHONE AChurn40   235-294-7081
    ADD_PHONE AChurn40   361-551-5980
    ADD_PHONE AChurn40   597-919-8261
    ADD_USER  ADuctil93    882 Anthony Ductile
    ADD_PHONE ADuctil93  375-449-4138
    ADD_PHONE ADuctil93  509-904-5217
    ADD_PHONE ADuctil93  644-036-2649
    ADD_USER  AFluenc43    682 Andrew Fluency PhD
    ADD_PHONE AFluenc43  495-712-4764
    ADD_PHONE AFluenc43  737-246-2569
    ADD_USER  AInterv57     13 Aiden Interval
    ADD_PHONE AInterv57  081-142-5426
    ADD_PHONE AInterv57  183-790-7235
    ADD_PHONE AInterv57  855-670-4758
    ADD_USER  AJugate14  38987 Austin Jugate
    ADD_PHONE AJugate14  174-351-3757
    ADD_PHONE AJugate14  610-205-1413
    ADD_PHONE AJugate14  856-562-1336
    ADD_USER  BBonifa55     93 Brianna Boniface
    ADD_PHONE BBonifa55  008-672-3102
    ADD_USER  CBarge68   24776 Chase Barge
    ADD_USER  DIneffi14  37842 Daniel Inefficient
    ADD_PHONE DIneffi14  029-131-8159
    ADD_PHONE DIneffi14  462-602-7283
    ADD_PHONE DIneffi14  569-485-8923
    ADD_USER  GMax14       235 Gabriel Max Set
    ADD_PHONE GMax14     556-830-7531
    ADD_USER  IParks92     696 Isaac Parks
    ADD_PHONE IParks92   119-480-9038
    ADD_PHONE IParks92   177-181-8465
    ADD_USER  JEcho91    11706 James Echo
    ADD_USER  NSvelte62     59 Noah Svelte
    ADD_USER  OMauve70    6464 Oliver Mauve
    ADD_PHONE OMauve70   120-797-9587
    ADD_PHONE OMauve70   364-503-8235
    ADD_PHONE OMauve70   451-559-9059
    ADD_USER  TVade56        2 Taylor Vade
    ADD_PHONE TVade56    355-887-8304
    ADD_PHONE TVade56    606-440-6857
    ADD_PHONE TVade56    914-780-5061
    MARK_USED 6ZzSTTdUaCDy6N 7fClHDlcNlxNpl F3W9dZq4NWCp3F jqivzc4eRM0Jt9 sHDNCtoOnMhctK
    UNIX> 
    
    Now let's look at the second -- it performs a bunch of commands, and writes six files -- f1.txt through f6.txt
    UNIX> cat /home/jplank/cs202/Labs/Lab7/Gradescript-Examples/050-B.txt
    REDEEM ACamelb30 cancun
    WRITE f1.txt
    ADD_PHONE AEmery68 223-558-4601
    REDEEM OMauve70 silver
    ADD_PHONE AChurn40 914-780-5061
    WRITE f2.txt
    WRITE f3.txt
    REDEEM DIneffi14 silver
    REDEEM OMauve70 dogo
    REDEEM AJugate14 spinner
    SHOW_PHONES BBonifa55
    DELETE_USER NSvelte62
    ADD_USER CBarge68 21 James Sanitate
    WRITE f4.txt
    REDEEM AChurn40 dogo
    WRITE f5.txt
    TEXT_CODE 914-780-5061 AIV9qdDuoE1Lsz
    REMOVE_PHONE ACamelb30 590-448-0257
    REDEEM AJugate14 dogo
    REMOVE_PHONE ACamelb30 702-497-7232
    WRITE f6.txt
    UNIX> 
    
    Let's run my program on it. There is some output, so let's examine it:
    UNIX> /home/jplank/cs202/Labs/Lab7/bin/cp_tester /home/jplank/cs202/Labs/Lab7/Gradescript-Examples/050-*.txt
    ADD_PHONE: Either the user (AEmery68) doesn't exist,
               or the phone number (223-558-4601) is already assigned
    ADD_PHONE: Either the user (AChurn40) doesn't exist,
               or the phone number (914-780-5061) is already assigned
    008-672-3102
    ADD_USER CBarge68 unsuccessful
    UNIX> 
    
    First, let's verify the first error statement by looking for AEmery68 and 223-558-4601 in the two input files. As you can see, we try to set AEmery68's phone number, and there's no such user:
    UNIX> egrep 'AEmery68|223-558-4601' /home/jplank/cs202/Labs/Lab7/Gradescript-Examples/050-*.txt
    /home/jplank/cs202/Labs/Lab7/Gradescript-Examples/050-B.txt:ADD_PHONE AEmery68 223-558-4601
    UNIX> 
    
    Let's verify the second error statement. Now you can see that 914-780-5061 was already assigned to TVade56.
    UNIX> egrep 'AChurn40|914-780-5061' /home/jplank/cs202/Labs/Lab7/Gradescript-Examples/050-*.txt
    /home/jplank/cs202/Labs/Lab7/Gradescript-Examples/050-A.txt:ADD_USER  AChurn40   21934 Audrey Churn
    /home/jplank/cs202/Labs/Lab7/Gradescript-Examples/050-A.txt:ADD_PHONE AChurn40   235-294-7081
    /home/jplank/cs202/Labs/Lab7/Gradescript-Examples/050-A.txt:ADD_PHONE AChurn40   361-551-5980
    /home/jplank/cs202/Labs/Lab7/Gradescript-Examples/050-A.txt:ADD_PHONE AChurn40   597-919-8261
    /home/jplank/cs202/Labs/Lab7/Gradescript-Examples/050-A.txt:ADD_PHONE TVade56    914-780-5061
    /home/jplank/cs202/Labs/Lab7/Gradescript-Examples/050-B.txt:ADD_PHONE AChurn40 914-780-5061
    /home/jplank/cs202/Labs/Lab7/Gradescript-Examples/050-B.txt:REDEEM AChurn40 dogo
    /home/jplank/cs202/Labs/Lab7/Gradescript-Examples/050-B.txt:TEXT_CODE 914-780-5061 AIV9qdDuoE1Lsz
    UNIX> 
    
    The phone number 008-672-3102 was printed out. Let's look for it in the input, and when we find that it belongs to BBonifa55, let's look for BBonifa55. As you can see, we gave the command "SHOW_PHONES BBonifa55", which is what printed "008-672-3102".
    UNIX> grep 008-672-3102 /home/jplank/cs202/Labs/Lab7/Gradescript-Examples/050-*.txt
    /home/jplank/cs202/Labs/Lab7/Gradescript-Examples/050-A.txt:ADD_PHONE BBonifa55  008-672-3102
    UNIX> grep BBonifa55 /home/jplank/cs202/Labs/Lab7/Gradescript-Examples/050-*.txt
    /home/jplank/cs202/Labs/Lab7/Gradescript-Examples/050-A.txt:ADD_USER  BBonifa55     93 Brianna Boniface
    /home/jplank/cs202/Labs/Lab7/Gradescript-Examples/050-A.txt:ADD_PHONE BBonifa55  008-672-3102
    /home/jplank/cs202/Labs/Lab7/Gradescript-Examples/050-B.txt:SHOW_PHONES BBonifa55
    UNIX> 
    
    Last, there was an error statement: "ADD_USER CBarge68 unsuccessful". Let's grep for CBarge68, and we can see that that username existed and we tried to add it a second time.
    UNIX> grep CBarge68 /home/jplank/cs202/Labs/Lab7/Gradescript-Examples/050-*.txt
    /home/jplank/cs202/Labs/Lab7/Gradescript-Examples/050-A.txt:ADD_USER  CBarge68   24776 Chase Barge
    /home/jplank/cs202/Labs/Lab7/Gradescript-Examples/050-B.txt:ADD_USER CBarge68 21 James Sanitate
    UNIX> 
    
    Let's make the directory correct_dir and move the six files there:
    UNIX> mkdir correct_dir
    UNIX> mv f?.txt correct_dir
    UNIX> ls correct_dir
    f1.txt	f2.txt	f3.txt	f4.txt	f5.txt	f6.txt
    UNIX> 
    
    Now, let's run the cp_tester in bin:
    UNIX> bin/cp_tester /home/jplank/cs202/Labs/Lab7/Gradescript-Examples/050-*.txt
    ADD_PHONE: Either the user (AEmery68) doesn't exist,
               or the phone number (223-558-4601) is already assigned
    ADD_PHONE: Either the user (AChurn40) doesn't exist,
               or the phone number (914-780-5061) is already assigned
    008-672-3102
    ADD_USER CBarge68 unsuccessful
    UNIX> 
    
    The output is identical, so that's good. However f1.txt through f6.txt don't match the ones in correct_dir, because this cp_tester implements Write() differently:
    UNIX> ls -l correct_dir/f1.txt
    -rw-r--r--. 1 jplank jplank 2020 Oct 22 14:58 correct_dir/f1.txt
    UNIX> ls -l f1.txt
    -rw-r--r--. 1 jplank jplank 2060 Oct 22 15:07 f1.txt
    UNIX> head correct_dir/f1.txt
    PRIZE     dogo         570      3 Club Dogo 12-Month Subscription
    PRIZE     habitat       35    100 Donation to Habitat for Humanity
    PRIZE     silver      1100      2 Two DMC Theatres Silver Experience movie tickets
    PRIZE     spinner      750      4 Multi-Function Salad Spinner and Chopper
    ADD_USER  ACamelb30  35158 Arianna Camelback
    ADD_PHONE ACamelb30  590-448-0257
    ADD_PHONE ACamelb30  596-598-2816
    ADD_PHONE ACamelb30  702-497-7232
    ADD_USER  AChurn40   21934 Audrey Churn
    ADD_PHONE AChurn40   235-294-7081
    UNIX> head f1.txt
    MARK_USED 6ZzSTTdUaCDy6N
    MARK_USED 7fClHDlcNlxNpl
    MARK_USED F3W9dZq4NWCp3F
    MARK_USED jqivzc4eRM0Jt9
    MARK_USED sHDNCtoOnMhctK
    ADD_USER  ACamelb30  35158 Arianna Camelback
    ADD_PHONE ACamelb30  590-448-0257
    ADD_PHONE ACamelb30  596-598-2816
    ADD_PHONE ACamelb30  702-497-7232
    ADD_USER  AChurn40   21934 Audrey Churn
    UNIX> 
    
    So, what I do is append "WRITE your_dir/f1.txt" to the end of f1.txt, create the directory your_dir/f1.txt and then I run my cp_tester on it. If the state of f1.txt is correct, regardless of formatting, then your_dir/f1.txt should match correct_dir/f1.txt exactly (because they were both created by my program):
    UNIX> mkdir your_dir
    UNIX> echo "WRITE your_dir/f1.txt" >> f1.txt
    UNIX> /home/jplank/cs202/Labs/Lab7/bin/cp_tester f1.txt
    UNIX> ls -l your_dir
    total 4
    -rw-r--r--. 1 jplank jplank 2020 Oct 22 15:14 f1.txt
    UNIX> diff your_dir/f1.txt correct_dir/f1.txt
    UNIX> 
    
    I hope that helps you understand what the gradescript is doing.