Problem: Scramble (Part 1)

This course’s philosophy on academic honesty is best stated as "be reasonable." The course recognizes that interactions with classmates and others can facilitate mastery of the course’s material. However, there remains a line between enlisting the help of another and submitting the work of another. This policy characterizes both sides of that line.

The essence of all work that you submit to this course must be your own. Collaboration on problem sets is not permitted except to the extent that you may ask classmates and others for help so long as that help does not reduce to another doing your work for you. Generally speaking, when asking for help, you may show your code to others, but you may not view theirs, so long as you and they respect this policy’s other constraints. Collaboration on the course’s test and quiz is not permitted at all. Collaboration on the course’s final project is permitted to the extent prescribed by its specification.

Below are rules of thumb that (inexhaustively) characterize acts that the course considers reasonable and not reasonable. If in doubt as to whether some act is reasonable, do not commit it until you solicit and receive approval in writing from the course’s heads. Acts considered not reasonable by the course are handled harshly. If the course refers some matter for disciplinary action and the outcome is punitive, the course reserves the right to impose local sanctions on top of that outcome that may include an unsatisfactory or failing grade for work submitted or for the course itself. The course ordinarily recommends exclusion (i.e., required withdrawal) from the course itself.

If you commit some act that is not reasonable but bring it to the attention of the course’s heads within 72 hours, the course may impose local sanctions that may include an unsatisfactory or failing grade for work submitted, but the course will not refer the matter for further disciplinary action except in cases of repeated acts.

Your work on this problem set will be evaluated along four axes primarily.

To obtain a passing grade in this course, all students must ordinarily submit all assigned problems unless granted an exception in writing by the instructor.

First, log into cs50.io and execute

within a terminal window to make sure your workspace is up-to-date.

Then, execute

at your prompt to ensure that you’re inside of chapter3 (which is inside of workspace which is inside of your home directory). Then execute

to download this problem’s distro. Unzip the ZIP file (remember how?) and then delete the ZIP file from your chapter3 directory. Navigate into your newly-created scramble directory (remember how?) and type:

You should see that your directory contains two files.

Scramble was^[1] a game, popular on smartphones, that challenges you to find as many words as possible in a 4x4 grid of letters before a timer expires. Each pair of letters in a word can be adjacent horizontally, vertically, or diagonally. Below, for instance, is what the modern version of the game looks like on an Android phone.

Present are words like THIS, SING, GEAR, HIS, RED, along with many other words.

In your terminal prompt, execute:

in order to try out the staff’s implementation of scramble. You should see a 4x4 grid filled with letters. As soon as you spot a word, type it and hit Enter. If it’s indeed a word in the grid (and in a dictionary of English words), your score will increase 1 point for each letter in the word. (Good job!) By default, you’ll have 30 seconds to find as many words as you can. You won’t see the clock ticking, but each time you input a word, you’ll see how many seconds you have left. As soon as time’s run out, you’ll be allowed to type one last word. (To quit the game early, hit ctrl-c.)

Now execute again:

Odds are the grid of letters changed? That’s because the distribution code uses rand. But what if you don’t want the grid’s letters to change each time you run scramble, particularly while debugging? No problem, simply execute

to play grid #1, or

to play grid #2, etc. That otherwise optional command-line arguments will be used as a "seed" for rand in order to perturb its output.

Time to take a break from playing! Open up scramble.c. The challenge at hand in this problem is to complete this game’s implementation. But first, let’s take a tour.

Notice first that atop scramble.c are a bunch of constants. Take note of the comments above each. Recall that declaring as constants values that you intend to use multiple times throughout your code tends to be good practice, so that you can change the value as needed in a single place.

Next, below those constants are some global variables. Global variables tend to be frowned upon (because there’s usually a cleaner way to achieve some goal). But when the sole purpose of a file is to implement some program, as is the case here with scramble.c, it’s not unreasonable to use globals to avoid passing around particularly important values again and again among several functions. For instance, we’ve declared grid as a global simply because so many functions will need access to it anyway, as you’ll eventually see.

Notice next how we’ve utilized typedef and struct (both of which are quite new!) to declare our very own data type called word, inside of which is a bool and an array. We’ll use a whole bunch of those structures in order to keep track of the words in that dictionary you downloaded (and whether the user has found them on the grid). Soon enough, we’ll learn more about the struct keyword and how to create our own data types. For now, take for granted that it’s possible, and consider it a sneak preview of things to come.

Below word, meanwhile, is dictionary, which we’ve declared as a struct without using typedef. The result is that this program will have just one dictionary structure, inside of which is an int and an array of many elements of type word.

Consider the prototypes below dictionary a sneak preview of the functions to come!

Incidentally, take care not to change any code related to logfile, which we use to automate some tests of your code!

Next read through main, focusing first on the comments and then on the code. If unsure at first glance what some line does, take some time to figure it out. It’ll be a lot easier to write new code if you understand the code that’s already there! If unfamiliar with some function, try to find it on CS50 Reference, else consult its "man page."

For instance, to pull up the manual for atoi, execute the below.^[2]

Notice, incidentally, how we’re utilizing some "ANSI color codes" in main in order to output red text when the game’s timer expires. They’re a bit cryptic, to be sure, but pretty easy to use. See this link for other colors.

Also, while debugging your program, you might want to comment out the call to clear in main so that you can see everything printed by printf, without anything disappearing.

Next read through each of the functions below main. Don’t fret if you don’t understand find and crawl, but do take a stab at reading through them. It turns out that crawl implements a "recursive" algorithm (whereby crawl calls itself) that searches the grid horizontally, vertically, and diagonally for a particular word, "marking" letters temporarily as it visits them so that it doesn’t accidentally get caught in an infinite loop.

Meanwhile, initialize might look a bit intimidating, but spend some time figuring out how it goes about initializing the grid with a distribution of letters. The man page for rand (albeit a bit cryptic itself) might help you figure out all the arithmetic.

Finally, load definitely has some new syntax, particularly FILE. We’ll revisit FILE and more in the weeks to come. For now, know that load simply loads a whole bunch of words, one per line, from a file into an array.

Hm, it seems we forgot^[3] to implement draw, lookup, and scramble. Oops!

Suffice it to say we need your help finishing this implementation of scramble! And just a couple other favors, too, if you don’t mind!

Now you can play (well, maybe after some debugging) your own version of scramble!

Completing the submission process for Chapter 3 onward requires that you have turned in all problems from Chapters 0, 1, and 2.