Homework 4

Due: November 25, 2019
Points: 100

You can turn this in late, until Monday, December 2 (the day school resumes after Thanksgiving), for 80% of your score (that is, a 20% deduction).

UNIX/Linux Questions

Please put the answers to these two questions in a text file called linux.txt or a PDF file called linux.pdf.

(20 points) On December 25, 2019, at 00:00:00 PST, how many seconds since January 1, 1970, 00:00:00 UTC, have passed? (Hint: look at the program date(1).)
(20 points) How do I find the login names and times of the people currently logged into the system“pc12.cs.ucdavis.edu”, and also where they logged in from?
(10 points) How do I delete a file named -i?

C Programming

(50 points) We will do the next step in the Game of Life program we began in Homework 2. For reference, the program life2.c in the directory /home/bishop/hw4-programs reads in the file given on the command line and draws it and the border. You can use that, or the one you did for homework 3.

The next step is to transform the board into the next generation. Each tranformation is a step. Recall the rules are as follows. Each square on the board may be populated (indicated by an ‘O’) or unpopulated (indicated by an ‘X’). The neighbors of a cell are the cells that adjoin it vertically, horizontally, or diagonally. At each step, the following transformations are applied to all the cells.
1. If a populated cell adjoins less than 2 other populated cells, or more than 3 populated cells, it becomes unpopulated.
2. If a populated cell adjoins 2 or 3 populated cells, it remains populated.
3. If an unpopulated cell adjoins exactly 3 populated cells, it becomes populated.
program will take the file with the predetermined pattern as its only argument. It is to print out the initial board (generation 0), and run for 50 generations (steps), printing out the board every 5 generations (so it should print generations 0, 5, 10, …, 50).

As an example, given the input file containing:
```
XOX
XOX
XOX
```
he output boards would be (ellipses indicate omitted output):
```
Generation 0:
-----
|XOX|
|XOX|
|XOX|
-----
Generation 5:
-----
|XXX|
|OOO|
|XXX|
-----
```
…
```
Generation 50:
-----
|XOX|
|XOX|
|XOX|
-----
```
As before, the board dimensions will never be more than 100 rows and 100 columns.

The output is to be written to the standard output. If there are no problems, your program is to return an exit status code of 0; otherwise, it is to return an exit status code of 1. Successful output looks as above. The following are the error messages:
- If malloc(3) fails, use perror(3) to print the message. If, for example, the return value of malloc is stored in p, then you would do the test as:
```
if (p == NULL) perror(s);
    …
```
  where p holds the return value of malloc and s is the string you are saving in the allocated space.
- If there are not exactly 2 command-line arguments (the program name and the file containing the pattern for the board), use an fprintf of the following form:
```
fprintf(stderr, "Usage: %s board_pattern\n", argv[0]);
```
- If opening the file fails, use perror to print an error message, like this:
```
perror(fname);
```
  where fname is the name of the file that you were trying to open.
- If a line in the file is of the wrong length, use an fprintf of the following form:
```
fprintf(stderr, "%s: line %d is wrong length\n", fname, lineno);
```
  where fname is the name of the file and lineno is the line number of the bad line.
- If a line in the file contains an invalid character, use an fprintf of the following form:
```
fprintf(stderr, "%s: bad character ’%c’ in line%d\n", fname, ch, lineno);
```
  where fname is the name of the file, ch is the invalid character, and lineno is the line number of the bad line.
To turn in: Put this program into a file called life3.c; turn it in as directed below. If you want to submit two files, that is, have this in a separate file, call the main one life3.c and the other file(s) init3n.c, where n is a single digit (for example, init30.c). Turn it in to Gradescope; you can do this as many times as you like, up to the due date, and we will grade the last one you submit.

Extra Credit

(30 points) For the program you wrote in problem 3, add the following four command-line options:
- -n followed by an integer (with or without intervening space): number of generations to run the program for
- -p followed by an integer (with or without intervening space): print the board at intervals of this many
The integers must be positive. For example, running
```
life3ex -n 100 -p 10 board
```
would begin with the pattern in board, run it for 100 generations, printing every 10th one (that is, it would print generations 0, 10, 20, …, 10, where generation 0 is the initial configuration). Always print the initial and final configurations.

In addition to everything for the program in life3.c, if either option is not followed by a number, use an fprintf of the following form:
```
fprintf(stderr, "%s: %c must be followed by a positive number\n", fname, option);
```
where fname is the name of the file and option the option involved, and if a bad option is given, use an fprintf of the following form:
```
fprintf(stderr, "%s: %c: invalid option\n", fname, option);
```
where fname and option are as above.

To turn in: Put this program into a file called life3ex.c and submit it to Gradescope.

Matt Bishop
Office: 2209 Watershed Sciences
Phone: +1 (530) 752-8060
Email: mabishop@ucdavis.edu

ECS 36A, Programming and Problem Solving
Version of November 14, 2019 at 8:14PM

You can also obtain a PDF version of this.