Summary:
This laboratory provides experience retrieving data from text files using C.
Citation:
This laboratory was copied (nearly verbatim) from
a laboratory by Henry Walker.
Useful Files:
Contents:
The file cities.dat
contains several items of
information about large American cities. More specifically,
each entry consists of the name of the
city (line 1), the county or counties (line 2) and the state (line 3)
in which it is situated, the year in which it was incorporated (line 4),
its population as determined by the census of 1980 (line 5), its area in
square kilometers (line 6), an estimate of the number of telephones in the
city (line 7), and the number of radio stations (line 8) and television
stations (line 9) serving the city. Thus a typical entry reads as follows:
Albuquerque
Bernalillo
New Mexico
1891
331767
247
323935
14
5
A blank line follows each entry, including the last.
Rather than leaving you to do everything from scratch, we have prepared
citystats.c, a
simple C program that lets you analyze city data.
a. Create a new directory for this lab.
b. Make a copy of
cities.dat.
c. Display it on your workstation (using less or other
similar command).
d. Observe that you can edit cities.dat by using an editor,
such as xemacs, vi, or gedit.
e. Make a copy of
citystats.c.
a. Review the source code for citystats.c. Take notes
on the purpose of the various procedures, any data types defined,
anything else interesting you note about the code.
b. Change anything you deem appropriate to make it work with your
copy of the data and in your directory.
a. What do you expect a typical interaction with citystats
to be like?
b. Compile and run citystats to verify your answer.
In my experience, if you display all the data in the file, the last
entry appears twice (with some awkward variation). Fix the code so that
the problem doesn't happen.
Reread the source code for citystats.c to identify answers
to the following questions.
a. How does the program know which file to read?
b. How is each line of text read?
c. What does procedure readLine do?
d. Why is readLine used in readCity for
city.nme, while fscanf is used for
city.yar?
e. Why do you think readLine is defined?
How might this program differ if data were being read from the
user rather than from a file?
Why might someone complain about the algorithm used for
readLine?
a. Fill in the details for procedure incorporated, which will
scan the entire text file and print out the data on each city that was
incorporated before 1843.
b. Update incorporated so that it takes takes a year as
a parameter. Update the user interface so that it asks for that number.
The population density of a city is the ratio of population to
area. Fill in the details of populationDensity to print
out the the city with highest population density.
a. Fill in the details of media so that it determines which
city has the lowest per capita radio and television stations.
b. Write a variant of media that takes a maximum per-capita
media rate and prints all cities that have a per-capita rate
less than the given amount.
c. Expand our variant so that it also takes a filename as a parameter and
writes information about the matching cities to that file.
Allow citystats to take the name of the cities file and the
action to perform as command-line arguments.
Thursday, 27 September 2001 [Henry Walker]
Monday, 19 November 2001 [Henry Walker]
Tuesday, 4 February 2003 [Samuel A. Rebelsky]
- Copied.
- Reformatted and rearranged.
- Added names to problems.
Wednesday, 5 February 2003 [Samuel A. Rebelsky]
Friday, 7 February 2003 [Samuel A. Rebelsky]
;
Check with Bobby