MAT 420 C++ Programming Assignment

In-class exercise and homework for Tuesday, Nov. 6

Due Tuesday, Nov. 13.

Please email me a brief synopsis (a few sentences will suffice) by Thursday, Nov. 8 describing your project and the people you will work with on it. In-class presentations will be scheduled beginning Nov. 27 (after Thanksgiving).

The objective today is to learn how parse an execute line to make a standalone utility. To illustrate, consider the sort utility. You can say

sort -n file.dat

which causes sort to read its data from file.dat (the explicit redirection < file.dat is not necessary). The command line also includes an option, -n, that asks sort to treat its input as numeric strings. The sort utility is quite flexible, insofar as if the file name argument is omitted, then it reads from the standard input.

The use of command line arguments is extremely useful, because programs that use them can be readily used in scripts and pipelines. A common but poor practice is for programs to prompt for options from the terminal. (Consider the problem of having to sort 100 different data files with a sorting program that, for each file, forces you to answer prompts regarding the name of the input file, whether the data is numeric, whether you want the data to be sorted in ascending order, etc.) A well-designed set of command-line options allows users to get the behavior that they desire for any number of files and makes your programs easy to automate with a script.

Unix/Linux systems include a utility function, called getopt, that simplifies the process of parsing command-line options. (The Posix shell also has a built-in function of the same name to allow command-line parsing in shell scripts.)

Practice exercise. Here is a sample C++ program that reads a command line for two possible options, a and n. The latter takes one integer argument. You can compile this program with

g++ -ansi -Wall -Wextra command_line.cc -o command_line

Try running it as

./command_line -a -n10
./command_line -an8 xyz.txt

and so on. See what happens if you invoke it with options other than a and n. Experiment and try adding some options. You do not need to turn in this program.

Homework exercise. Write a C++ program that prints the mean, median, standard error and number of elements in the input. Your program should read from the standard input or from a file named on the command line, if present.

By default, the output is to be printed with 6 significant digits; but this must be changeable with the -p option; for instance, -p10 causes your program to display up to 10 significant digits. (Include checks for reasonable values for the argument.)
Your program prints output in the following order:
mean median standard-error n filename
where n is the number of elements in filename and standard-error is the usual estimator of the standard error of the mean.
By default, your program prints all five values above. Provide options to select them as follows:
- -m, print the mean only
- -M, print the median only
- -n, print the count (n) only
- -e, print the standard error only
The options can be concatenated; for example,
stats -Mn filename
prints
median n filename
Also include an option -h, which, if specified, prints a brief help message to the standard output summarizing the arguments and behavior and exits.

Here is a skeleton program to get you started.

Put your source code into a file called stats.cc. Your program should handle the case of empty input gracefully (i.e., not crash). In addition, your program must not generate any diagnostics when compiled with

g++ -ansi -Wall -Wextra stats.cc -o stats

(See the manual page for g++ for details on these options.)

See Koenig and Moo, p. 181, Section 10.5, for details and an illustration of the use of the ifstream facility.

Submission instructions

You will create one file for this assignment, stats.cc. Since there is only one file, you may email it directly as an attachment to

mat420hw at gmail.com

Please include your name in the subject line! Assignments are due by November 13.

Reading assignment

Please read Chapters 7 and 8 of Koenig and Moo. These topics will be the subject of the last two computer labs.