Homework 1
Caution
  • You are expected to work individually.
  • Due: Friday, September 12th at 11pm Baltimore time.
  • This assignment is worth 60 points.

Learning Objectives

Objectives
  • arithmetic operators
  • arrays
  • control structures
  • input collection and validation
  • version control using git

Overview

In this homework, you will write a program to keep track of geographic locations. Each location will be labeled with a single capital letter (in range ‘A’ to ‘Z’) and have associated with it a latitude and longitude pair. The program will allow the user to add and remove locations, list the locations currently stored along with their latitude and longitude, as well as compute the geographical distance between two locations.

Program Requirements

We will use 8 as the maximum number of stored locations that the program must handle. When the program starts, it displays a welcome message and then enters a command loop. The program presents a menu of options, which the user is then prompted to choose from by entering the number corresponding to the option. It must do error handling to make sure the option entered is an integer and a valid option value. Depending on the command, the program will then then prompt the user for the required input, which will also be validated. If the inputs are valid, the program then carries out the command and then continues the command loop by presenting the menu again. The program terminates when there are problematic inputs or the user chooses to quit. (See below for prompts and error handling details.)

There are five options the user may choose from:

Error Handling

In the following, the error code constants refer to those declared in the starter code provided. The program should handle errors as follows.

All error messages must end with a line break. You do not need to consider any other errors in your implementation.

Specifications, Development Requirements, and Hints

In the homework folder of your private repository (the one having the name in the form YEAR-TERM-student-JHED or my220repo), you should create a new subfolder named homework/hw1. Copy into that homework/hw1 subfolder the starter code file distance.c provided in the public repository, from folder homework/hw1. At the top of the file, add a comment with your six character alphanumeric Hopkins ID. (Please do not include your name or JHED so as to allow for blind grading.)

Use three parallel arrays to keep track of labels, latitudes, and longitudes. You’ll also need a variable to count how many different locations have been entered so that you know which elements of these arrays are used.

Make sure that your program consistently checks the return value of scanf so that it knows whether or not input was read successfully.

The starter code provided defines the constant M_PI. Use this value when converting latitudes and longitudes from degrees to radians before applying the distance formula provided above.

Throughout your work on this assignment, be sure to frequently add, commit (supplying meaningful messages) and push your changes to your personal repository. After you complete your work on the assignment, you will be asked to submit a gitlog.txt file, just as in Homework 0. However, we expect your log for this homework to show more activity.

Your code is always expected to compile without errors or warnings on the ugrad servers. Submissions which do not compile properly may earn zero points, so be sure to submit to Gradescope early and often! And once you get a good start on the assignment, always have some earlier compiling version of your work pushed to Github. Use the following line to compile your code: gcc -lm -std=c99 -pedantic -Wall -Wextra distance.c -o distance (the -lm option indicates that the compiler should link with the math.h library, since you should be using it for your trigonometric functions.) You can then run your program with the command ./distance.

Sample Runs

Caution

When you test your program in a terminal using the example inputs shown below, the result should be exactly what is shown below, including spacing. Note that

  • Each prompt should end with a space, but should not have a newline at the end, with the exemption of the prompt to enter type identifiers and durations.
  • Each output line indicating an error should end with a newline.

Here are several samples runs of the program on ugrad, where $ denotes the command prompt, and user input is shown in bold. Note that the first line shown below is the command you are expected to use as you compile your program (and the one that will be used by the graders). The compilation line should report zero errors and warnings, as demonstrated in these examples.

Example 1 (no input errors)

This example demostrates adding locations for Baltimore (B) and Washington (W), listing the locations, computing the distances between them, removing a location and re-listing.

$ gcc -lm -std=c99 -pedantic -Wall -Wextra distance.c -o distance
$ ./distance 
Welcome to the distance calculation program.
Please select an option:
[1] Add a location
[2] Remove a location
[3] List locations
[4] Compute distance
[0] Quit
Option: 1
Enter a label: B
Enter a latitude and longitude pair: 39.2904 -76.6122
Please select an option:
[1] Add a location
[2] Remove a location
[3] List locations
[4] Compute distance
[0] Quit
Option: 1
Enter a label: W
Enter a latitude and longitude pair: 38.9072 -77.0369
Please select an option:
[1] Add a location
[2] Remove a location
[3] List locations
[4] Compute distance
[0] Quit
Option: 3
B: (39.290400, -76.612200)
W: (38.907200, -77.036900)
Please select an option:
[1] Add a location
[2] Remove a location
[3] List locations
[4] Compute distance
[0] Quit
Option: 4
Enter a label: B
Enter a second label: W
Approximate distance in miles: 34.92
Please select an option:
[1] Add a location
[2] Remove a location
[3] List locations
[4] Compute distance
[0] Quit
Option: 2
Enter a label: B
Please select an option:
[1] Add a location
[2] Remove a location
[3] List locations
[4] Compute distance
[0] Quit
Option: 3
W: (38.907200, -77.036900)
Please select an option:
[1] Add a location
[2] Remove a location
[3] List locations
[4] Compute distance
[0] Quit
Option: 0
$

Example 2 (bad option)

$ gcc -lm -std=c99 -pedantic -Wall -Wextra distance.c -o distance
$ ./distance 
Welcome to the distance calculation program.
Please select an option:
[1] Add a location
[2] Remove a location
[3] List locations
[4] Compute distance
[0] Quit
Option: A
Error: Unable to read option.
$

Example 3 (bad label)

$ gcc -lm -std=c99 -pedantic -Wall -Wextra distance.c -o distance
$ ./distance 
Welcome to the distance calculation program.
Please select an option:
[1] Add a location
[2] Remove a location
[3] List locations
[4] Compute distance
[0] Quit
Option: 1
Enter a label: x
Error: Invalid label.
$

Example 4 (duplicate label)

$ gcc -lm -std=c99 -pedantic -Wall -Wextra distance.c -o distance
$ ./distance 
Welcome to the distance calculation program.
Please select an option:
[1] Add a location
[2] Remove a location
[3] List locations
[4] Compute distance
[0] Quit
Option: 1
Enter a label: B
Enter a latitude and longitude pair: 39.2904 -76.6122
Please select an option:
[1] Add a location
[2] Remove a location
[3] List locations
[4] Compute distance
[0] Quit
Option: 1
Enter a label: B
Error: Duplicate label.
$

Example 5 (label not found)

$ gcc -lm -std=c99 -pedantic -Wall -Wextra distance.c -o distance
$ ./distance 
Welcome to the distance calculation program.
Please select an option:
[1] Add a location
[2] Remove a location
[3] List locations
[4] Compute distance
[0] Quit
Option: 1
Enter a label: B
Enter a latitude and longitude pair: 39.2904 -76.6122
Please select an option:
[1] Add a location
[2] Remove a location
[3] List locations
[4] Compute distance
[0] Quit
Option: 1
Enter a label: W
Enter a latitude and longitude pair: 38.9072 -77.0369
Please select an option:
[1] Add a location
[2] Remove a location
[3] List locations
[4] Compute distance
[0] Quit
Option: 4
Enter a label: T
Error: Label not found.
$

Example 6 (unable to read coordinates)

$ gcc -lm -std=c99 -pedantic -Wall -Wextra distance.c -o distance
$ ./distance 
Welcome to the distance calculation program.
Please select an option:
[1] Add a location
[2] Remove a location
[3] List locations
[4] Compute distance
[0] Quit
Option: 1
Enter a label: L
Enter a latitude and longitude pair: x y
Error: unable to read coordinates.
$

Example 7 (coordinate out of range)

$ gcc -lm -std=c99 -pedantic -Wall -Wextra distance.c -o distance
$ ./distance 
Welcome to the distance calculation program.
Please select an option:
[1] Add a location
[2] Remove a location
[3] List locations
[4] Compute distance
[0] Quit
Option: 1
Enter a label: L
Enter a latitude and longitude pair: 90.01 0.0
Error: coordinate out of range.
$
Tip

There may be other ways for the input to be malformed, besides the ways shown above. You must be careful to check for all the various ways it might be malformed.

Starter File and Testing

It is your responsibility to test a variety of valid input situations as well as invalid inputs. Make sure to test that every possible error condition detailed in the specifications is handled as specified. Think critically as an adversary for other problems or edge cases that your program might encounter, and test that they are handled appropriately.

For this first real assignment, we are providing a starter file distance.c and sample input files with matching output files that you can use to check whether your prompts and outputs are programmed exactly as expected. This is the type of testing that our autograder will usually perform in public and hidden tests. In order to access the samples you will need to download them from our public course repo using commands similar to those in exercise 3b, assuming you have successfully cloned that repository. If not, complete exercises 3a and 3b and ask for help in office hours or class if needed.

First, log into the ugrad system and navigate into your clone of the cs220-xxx-public repo (where xxx represents the current semester.) Do a git pull to get the latest files we have provided. Then, using the unix command cp (copy) along with customized file paths based on your file directory set-up, you’ll want to copy from cs220-xxx-public/homework/hw1/ to the directory where you are coding your solution to this assignment.

When you’re ready to test your output locally, compile and run on the input file using input redirection, saving the stdout output to file my_output_xx.txt (where xx refers to the particular number of file you’re testing.) For example, to check with the first sample input, run the command:

$ ./distance < sample_input_01.txt > my_output_01.txt

Now use the unix diff command to compare our output file to yours. This does an exact character comparison. The output should be nothing if the files match exactly as shown below.

$ diff sample_output_01.txt my_output_01.txt
$

If the output files don’t match, then you will be shown which lines differ. Sometimes the difference may only be a space that is invisible to us, but that could cause an autograder test to fail. What is shown is the output in the first file (sample_output_01.txt) indicated by lines that start with < and the output in the second file (my_output_01.txt) indicated by >. Each pair of lines that differ start with the line number(s) in the first file and the line number(s) of the mismatches in the second file. It is generally recommend that you use the reference file as the first argument to diff for consistent interpretation of these results.

You can use this style of testing to make your assignment process smoother throughout the semester. We recommend writing multiple small input files so you can easily re-run them on your evolving solution with input redirection to see if you get the right output. However, we won’t usually provide either the input or the reference output for you. You’ll need to figure out what that should be.

Style

You should also make sure that your code has good style. You can look at the coding style guidelines here from a course you may take later that also applies to this course. In brief, you should make sure that your submission is well formed, readable, consistently styled, and documented as follows:

For this homework, since declaring functions has not yet been covered in class, you are not required to write your own helper functions; i.e. you can have your entire program under the main function. However, if you would like to declare your own functions you are permitted (and encouraged) to do so.

Submission

Create a .zip file named hw1.zip which contains only distance.c and gitlog.txt. (Do not zip your entire hw1 folder - only these two files.) Copy the hw1.zip file to your local machine and submit it as Homework 1 on Gradescope.

Recall you can create your gitlog.txt file by running git log > gitlog.txt.

When you submit, Gradescope conducts a series of automatic tests. These tests do basic checks like making sure that you submitted the right files and that your .c file compiles properly. If you see error messages here (look for red), address them and resubmit until you pass them. Some of the error messages will show results similar to the diff in Testing example above.

Tip

You may re-submit any number of times prior to the deadline; only your latest submission will be graded.

Info

Review the course syllabus for late submission policies. Remember that you can use at most 2 late days from your remaining budget for any one assignment and any portion of a day counts as one whole day.

Grading

Two notes regarding automatic checks for programming assignments:

No-compile Policy

Remember that if your final code submission does not compile, you will receive a zero score for the assignment.

The 60 points for this assignment will be distributed roughly as follows when we grade:

Please plan accordingly, and practice incremental coding and testing for best results!