关于c:COMP1711XJCO1711-解析

University of Leeds School of Computing
Procedural Programming COMP1711/XJCO1711
Semester 1, 2020-2021
Coursework 3
100 Marks (40% of the total module mark)
To be submitted before: 23:00 (UK time) on 11 December 2020
Late penalties: 5% will be deducted from the overall mark of this coursework for every
late day
Skills Tested
This coursework will test your ability to write C code that correctly uses structures, character strings,
pointers, and file i/o. You will also learn how a program can be divided across multiple source files.
The Brief
You will write a program that allows people to name pairs of stars in a hypothetical universe by their
names.
The Details
An astronomer wanted to surprise their spouse on their anniversary by showing them a simulation of
the Big Bang on a computer, then naming the closest pair of stars created by this Big Bang with their
names. Big Bang is the name of a cosmological theory that assumes that the universe started from the
expansion of a single very high-density singularity.
Fortunately, the program is not supposed to go anywhere close to a real simulation of the Big Bang.
For the purposes of this simple program, our Big Bang simply fills a flat rectangular space with stars
scattered at random positions. The program then allows a user to find the closest pair of unnamed
stars in this universe and assign the user’s name to the first star in this pair, and the name of the user’s
spouse to the second star.
The Task
Write a command driven program that accepts the following commands:
The bang command
This command creates a hypothetical universe comprised of stars only. The stars should be randomly
scattered across the universe.
We are assuming that the universe is flat and rectangular and is 60 light years long and 30 light years
wide. A light year is a unit of measure of distance and is equal to the distance that light can travel in
one year (5.879×1012 miles). Do not get daunted by this jargon, just assume that your space is a
rectangle 60 units long and 30 units wide.
The bang command takes one integer argument representing the number of stars to be created. For
example, if the player types:

bang 100
the program will create 100 stars randomly distributed within the universe (the 60×30 rectangle). The
position of a star is determined by two coordinates, x and y. No two stars should have the same
coordinates. For simplicity, assume that x and y are both integers. Also assume that the origin of the
coordinate system is at the upper left corner of the universe, with the x axis pointing to the right, and
the y axis pointing downwards, as shown in the following figure:
Note that in the above figure, the aspect ratio (ratio of height to width) of the universe is distorted.
The reason for this will be explained later on.
It is important to keep the origin of the coordinate system at the upper left corner, and the directions
of the axes as shown. Changing these assumptions could make it more difficult to implement the
drawing functions of the game.
Each star must have a unique serial number (id) generated by the program when the universe is
created. Initially, stars have no names, but players can later name stars using the name command (see
below).
If the bang command is issued again (after a universe has been created), the existing universe is
destroyed and a new one is created in its place.
The list command
This command simply prints a list of all stars in the universe. For each star, the command prints the
star’s serial number, name (if the star is named), and the star’s x and y coordinates. For example, if
the player types:
list
the program prints a list similar to this one:
Note that in the above list none of the stars has a name, which is the situation when a new universe
is created.
The name command
This command is used to find the closest pair of stars that has not been named yet and allow the user
to name this pair. The program prompts the user to enter their name and that of their spouse. The
first star in the pair is named after the player, and the second is named after the player’s spouse. Once
a pair of stars is named, this pair is permanently reserved for its‘owners’and cannot be renamed by
other players. Here is an example of the name command:
However, if all pairs have already been named, the program prints a message similar to this:
The pairs command
This command prints a list of all star pairs that have been named so far. For each pair, the program
prints the pair’s number, the distance between the two stars of this pair, and the details of the two
stars. Here is an example:
The draw command
This command is used to draw the universe. Named stars appear as asterisks (*), while unnamed stars
appear as dots (.). Here is an example:
You will NOT be using any graphics library to draw the universe. Instead, you will use a simple trick to
convert the standard terminal to a primitive drawing window. This will be explained below.
The show command
This command is used to display the names of the couple who own a pair of stars. When this command
is executed the program prompts the user to enter their name as shown below
The program then searches for a pair of stars named after this user, and if a pair is found, the program
displays the names of the couple who own the pair under the stars of this pair, as shown in the
following example:
The save command
This command is used to save the universe. By this we don’t mean saving the universe from the evils
of a supervillain. Instead, this command saves the program’s data into a file. The command should
save all stars and all named pairs in the universe into a binary file called universe.bin located in the
program’s directory. Here is an example:
The load command
This command is used to load (read) saved data from the universe.bin file. When the command is
executed the program reverts to the point at which it was saved.
The quit command
This command is used to terminate the program.
Implementation Guidelines
Generating random numbers
To generate random values for star coordinates, you can use the rand function. This function is defined
in the <stdlib.h> library. When the function is called it returns a random integer between 0 and
RAND_MAX. The value of RAND_MAX is system dependent but is guaranteed to be at least 32767.
You can scale the random number returned by rand to any required range [0, x-1] by applying the
modulo operator on the value returned by the function, like this:
int r = rand() % x; // r is a random number in the range [0, x-1];
Unfortunately, the rand function is a pseudorandom number generator, which means that it will
always generate the same sequence of random numbers every time you run the program. To get a
different sequence each time, you can use the srand function (also defined in <stdlib.h>). The srand
function‘seeds’the random number generator with an initial value. By changing the initial value, we
can get different random number sequences. We need a value that is different every time we run the
program. This can be some distinctive runtime value, like the value returned by the time function
defined in the <time.h>. The time function returns the time in seconds that elapsed since some past
point in time. You should seed your random number generator only once at the beginning of your
program like this:
time_t t;
srand((unsigned) time(&t));
Using the terminal as a graphics window
To‘draw’the stars of the universe on the terminal, we will use a simple trick based on the fact that
the terminal prints characters in a rectangular grid of rows and columns. The cursor that determines
the position of the next character to be printed is initially at the top left corner of the terminal window.
When a single character is printed, the cursor moves exactly one column to the right. When the new
line character (‘\n’) is printed the cursor moves to the first column in the next row. The following figure
shows how the terminal will look like when 30 rows of characters, with 60 characters (columns) per
row, are printed.
In this sense, the terminal can be considered as a very coarse grid of‘pixels’, just like any other graphics
display. However, the elements of the grid are characters rather than pixels. Notice that the above
grid appears rather squarish although it has twice as many columns as it has rows. This is because the
height of the font used to display the characters is almost twice as its width. Most Latin fonts are like
this, but you may find one on your machine that is not.
To draw things on the terminal, you will need a two-dimensional array (matrix) of characters. We will
call this matrix the frame buffer because it will be used to prepare the frame (picture) of the universe
before printing it on the screen. Each row in this matrix corresponds to one row of characters on the
terminal. The frame buffer will have 31 rows and 61 columns, as shown below:
Now, to draw a star whose (x, y) coordinates are (4, 1) for example, we simply store the asterisk (*) in
row 1 and column 4 of the frame buffer as shown above. And, to‘draw’the letter X in location (57, 3)
we put‘X’in row 3 and column 57 of the frame buffer.
After all the stars of the universe are stored in their correct positions in the frame buffer, the whole
frame buffer can be displayed on the terminal in one go.
Submission Instructions
 Write the program in standard C. If you write your code in any other language, it will NOT be
marked, and you will get a zero for this coursework.
 Gradescope will be used to mark this coursework. Detailed instructions on how to prepare and
submit your code to Gradescope will be published on Minerva.
 Four files – called uni.h, graph.c, logic.c, and main.c – are provided for you to start developing
your code. Do not alter anything in uni.h and do not submit it to Gradescope.
 File uni.h contains some function prototypes. You must implement the body of these functions
in the graph.c, logic.c and main.c files. You will also need to use these functions to implement
the program functionality.
 Make sure that you fill in your name, University number, and the date you started working on
the assignment in the space provided at the top of each file.
 This is an individual project, and you are not supposed to work in groups or pairs with other
students.
 Please be aware that plagiarism in your code will earn you a zero mark and will have very
serious consequences. It is much better to submit your own partially finished work, than to
fall into the trap of plagiarism. We use software to detect plagiarism, so if you do work
with someone else, or submit someone else’s work it WILL be detected.
Finally, let’s hope that the astronomer’s wife will be impressed by the game after all this hard work.
Marking Scheme
Graphics Functions
Function clearBuffer () (4 marks)
Function plot () (2 marks)
Function peek () (2 marks)
Function writeAt () (6 marks)
Function showBuffer () (6 marks)
Program Logic Functions
Function findStarByXY () (5 marks)
Function bigBang () (12 marks)
Function pointDistance () (2 marks)
Function closestPair () (12 marks)
Function nameStar () (5 marks)
Function findPairByName () (4 marks)
Function saveUniverse () (6 marks)
Function loadUniverse () (6 marks)
Interface Functions and the User Interface
Function printStar () (2 marks)
Function listStars () (2 marks)
Function listPairs () (4 marks)
Function drawUniverse () (6 marks)
Function tagPair () (6 marks)
The user interface works correctly (8 marks)