This assignment makes use of files contained in this zip file. This assignment is due Tuesday, September 8.
In this assignment you will write a C filter program that formats a stream of input numbers into nicely organized columns. Your program will make use of command-line arguments and environment variables to determine parameters for the output formatting.
Write a C program called filter.c that reads from standard input and writes to standard output. The input to your program will be decimal numbers separated by white space. The output of your program will be the input numbers formatted into columns.
The decimal point of every number in a column must line up. The number of digits after a decimal point is called the precision of a decimal number. All the numbers in the output will have the same precision. The default precision for your output is 13 decimal places. If there is an environment variable called CS223HW1PRECISION, then the value of that variable overrides the default precision. If there is a command line parameter, then that command line parameter overrides both the environment variable (if there is one) and the default value of precision.
The default number of output columns for your output is three. If there is an environment variable called CS223HW1COLUMNS, then the value of that variable overrides the default number of columns. If there is a second command line parameter, then that command line parameter overrides both the environment variable (if there is one) and the default number of columns.
Your program should use the Standard C Library function getenv() to see if there are environment variables named CS223HW1PRECISION or CS223HW1COLUMNS. If either one exits, its string value should be converted to an integer value by using the Standard C Library function atoi() ("atoi" is an abbreviation of "ascii to integer")..
Your program will read in values from standard input by using the Standard C Library function scanf() and its associated formatting strings.
Your program will write formatted output numbers (with the decimal points lined up and the proper number of decimal digits) to standard output by using the Standard C Library function printf() and its associated formatting strings. (Hint: You will need to make use of the * character in your format strings.)
Formatted input and output is not as hard as it might seem by looking at the last few references. After a few examples, you quickly get the hang of it.
Here are a couple of examples. If the input stream to your program looks like this:
5163.1575670644243 6806.8180791650138
8977.2739646595655
2598.0792870876185 7162.5237586596268 6691.2041993469038
1043.6422009949033
6922.8216193121125 3.0480056154058 9926.6081118198181 100.3082369457076
5135.1567125461588 7808.2382885219886 1439.6542863246559 249.6179692983795
214.0065309610279 9280.5883968626968 2687.3871883297220
7612.8426770836513 6644.2027649769589 8364.5604419080173 4740.7550279244360
254.6181218909269 2500.3814813684498
2293.6803491317482 835.3306680501725
5962.7923215430155 9622.5988341929387 57.3069246498001
1557.9630726035341 8398.5614795373385 5958.4870143742182
2568.3835566270945 9935.9135715811644 3410.1040681173131
982.0299691763055
8393.5613269447913 9066.2766808069100 4896.4546037171549
7597.8422193060087 8551.5661488692895 1076.6432081057162
1911.3635059663686 7586.8418836024048 9282.8936429944770 4696.1433149204995
1388.0423596911528
1936.3642689291055 3408.4091921750542 3556.4137089144565
9241.8923917355878 5003.4578691976685 3366.7130954924160
4270.1303140354621 620.6292916653950 4700.7538071840572 1766.0538956877347
441.6238288521989 8153.8591875972779
then the default way to format this is with three columns and 13 digits of precision.
5163.1575670644243 6806.8180791650138 8977.2739646595655 2598.0792870876185 7162.5237586596268 6691.2041993469038 1043.6422009949033 6922.8216193121125 3.0480056154058 9926.6081118198181 100.3082369457076 5135.1567125461588 7808.2382885219886 1439.6542863246559 249.6179692983795 214.0065309610279 9280.5883968626968 2687.3871883297220 7612.8426770836513 6644.2027649769589 8364.5604419080173 4740.7550279244360 254.6181218909269 2500.3814813684498 2293.6803491317482 835.3306680501725 5962.7923215430155 9622.5988341929387 57.3069246498001 1557.9630726035341 8398.5614795373385 5958.4870143742182 2568.3835566270945 9935.9135715811644 3410.1040681173131 982.0299691763055 8393.5613269447913 9066.2766808069100 4896.4546037171549 7597.8422193060087 8551.5661488692895 1076.6432081057162 1911.3635059663686 7586.8418836024048 9282.8936429944770 4696.1433149204995 1388.0423596911528 1936.3642689291055 3408.4091921750542 3556.4137089144565 9241.8923917355878 5003.4578691976685 3366.7130954924160 4270.1303140354621 620.6292916653950 4700.7538071840572 1766.0538956877347 441.6238288521989 8153.8591875972779
On the other hand, if we use seven columns and only two digits of precision, the same input should produce the following output.
5163.16 6806.82 8977.27 2598.08 7162.52 6691.20 1043.64 6922.82 3.05 9926.61 100.31 5135.16 7808.24 1439.65 249.62 214.01 9280.59 2687.39 7612.84 6644.20 8364.56 4740.76 254.62 2500.38 2293.68 835.33 5962.79 9622.60 57.31 1557.96 8398.56 5958.49 2568.38 9935.91 3410.10 982.03 8393.56 9066.28 4896.45 7597.84 8551.57 1076.64 1911.36 7586.84 9282.89 4696.14 1388.04 1936.36 3408.41 3556.41 9241.89 5003.46 3366.71 4270.13 620.63 4700.75 1766.05 441.62 8153.86
In the zip file for this assignment you will find an program called source.c that you can use to test your program. The program source.c writes to standard output a stream of random decimal numbers (all with 13 digits of precision). The numbers are separated by random amounts of white space and there are a random number of numbers on each line of output. You can test your filter.c program by "piping" the standard output of source into the standard input of your filter. For example, the first output shown above might have been created by a command like the following.
> source | filter
On the other hand, the second output above could have been produced by the following two shell commands.
> set CS223HW1COLUMNS=7 > source | filter 2
or by the following single shell command.
>> source | filter 2 7
If you have never worked with filters and pipes before, the last command is equivalent to the following two commands (that use I/O redirection).
> source > temp > filter 2 7 < temp
The first command "redirects" the standard output from source into the temporary file temp and then the second command "redirects" the contents of temp into the standard input of filter. (How would you save the resulting output from the filter in a file called data.txt?) The piped version of the command has the advantage of not needing to use a temporary file.
In the zip file for this assignment you will also find two Windows executable programs called source.exe and filter.exe (and two Linux executable programs called source and filter) that you can use to demo this assignment on a Windows (respectively Linux) computer.
Here is an outline of how you can go about attacking this problem.
Turn in a zip file called CS223Hw1Surname.zip (where Surname is your last name) containing your version of filter.c.
This assignment is due Tuesday, September 8.
Below are some references about I/O redirection, command-line arguments and environment variables.