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Homework 1

Update 2/4: added a few clarifications

Learning Objectives

Overview

In this homework, you will write a program to help the user keep track of a collection of coins of arbitrary denominations.

Program Requirements

When the program starts, it prompts the user to enter the number of different coin denominations that will be used (“How many denominations?”). Then, for each coin denomination, it prompts the user for a one-letter identifier and the value of the coin (“Enter coin identifier and value in cents:”). Note that the coin identifiers are case-sensitive, so “d” and “D” are different identifiers. Also note that the value of the coin must be an integer (i.e., the program should represent coin values as integers.)

Once all of the coin identifiers and values are recorded, the program enters a command loop. Each time the program prompts the user to enter a command (“Enter a command:”), the user enters the one-letter name of the command, and if the command requires additional values to be entered, reads those values. It then carries out the command and if the command was not “q” (quit), continues the command loop.

There are four commands:

• The a command adds to the count of how many coins of a specified type are in the user’s collection. The a command is followed by the one-letter identifier of the type of coin to be added, followed by the integer count of how many of that type of coin should be added to the collection. For example a p 11 would add 11 of the type of coin identified by the letter “p” to the collection.
• The r command subtracts from the count of how many coins of a specified type are in the user’s collection. It behaves like the “a” command, except that the count of the specified type of coin is subtracted from the collection rather than added to the collection.
• The s command summarizes the user’s coin collection. The output is formatted as comma-separated values (CSV). First, a header line with the fields “Identifier”, “Face Value”, “Count”, and “Total Value” is printed. Then, for each kind of coin (in the order in which they were entered at the beginning of the program execution), an output line is printed with the coin identifier, coin face value, number of that type of coin in the user’s collection, and total value of that kind of coins in cents. For both the header line and the lines summarizing each kind of coin, fields are separated by comma (“,”) characters, with no space before or after each comma. At the end of the summary, a line reading “Overall value of collection: $X.YY” is printed, where X and YY indicate the number of dollars and cents in the overall value of the collection.
• The q command causes the command loop to terminate.

Note that the user could also terminate the command loop by typing ctrl-d when prompted for a command.

When the command loop terminates, the program prints a line with the text Bye! and then exits with the exit code 0.

Error Handling

The program should handle errors as follows.

If either

• the user doesn’t enter a valid value for the number of coin denominations when prompted, or
• the user doesn’t enter a valid identifier and value for a coin denomination when prompted, or
• the user doesn’t enter a valid identifier and count after an a or r command,

then the program should print the line “Invalid input” to stderr and exit with the exit code 1.

If the user enters a coin identifier as part of an a or r command that is not one of the identifiers entered by the user prior to the command loop, the program should print the line “Unknown coin identifier” to stderr and exit with the exit code 2. Note that the “Unknown coin identifier” should only be printed if the coin identifier and count were both read successfully.

If the user enters a command character that is not one of a, r, s, or q, then the program should print the line “Invalid command” to stderr and exit with the exit code 3.

If no errors occur and the program completes normally, it should exit with the exit code 0.

Note that all of your code can be in a single main function, so a return statement will exit the program. E.g., the statement

return 1;

will exit the program with the exit code 1. (In future assignments, we will expect you to write functions to modularize your program, but you don’t need to use functions for this assignment.)

Note that you do not need to handle the following kinds of errors:

• The user specifies that there are fewer than 1 or more than 20 coin denominations
• The user enters the same coin identifier more than once when entering the coin denominations
• The user uses the “r” command in a way that would cause the count of a particular kind of coin to drop below 0

Hints and Specifications

The program should allow the user to enter up to 20 coin denominations. You should use arrays to keep track of the identifiers for each type of coin and their face values. For example,

char identifiers[MAX_DENOMINATIONS];
int values[MAX_DENOMINATIONS];

You’ll also want to have a variable indicating how many different types of coins there are, so that you know which elements of these arrays are used.

It will also make sense to have an array keeping track of how many coins of each type are in the user’s collection.

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

Keep in mind that error messages should be printed to stderr and not stdout.

Development Requirements

In the homework folder of your private repository (2024-spring-student-JHED), you should create a new subfolder named homework/hw1. In that homework/hw1 subfolder, you will create your program in a new C source file named coins.c. 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.)

Throughout your work on this assignment, be sure to frequently add, commit (supplying meaningful messages) and push your changes to your personal git 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.

Recall that 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 up to Github.

Example Runs

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 below:

Example 1

$ gcc -std=c11 -pedantic -Wall -Wextra coins.c
$ ./a.out
How many denominations? 5
Enter coin identifier and value in cents: p 1
Enter coin identifier and value in cents: n 5
Enter coin identifier and value in cents: d 10
Enter coin identifier and value in cents: q 25
Enter coin identifier and value in cents: D 100
Enter a command: a p 37
Enter a command: a q 5
Enter a command: a D 4
Enter a command: r q 2
Enter a command: s
Identifier,Face Value,Count,Total Value
p,1,37,37
n,5,0,0
d,10,0,0
q,25,3,75
D,100,4,400
Overall value of collection: $5.12
Enter a command: q
Bye!

Example 2 (Canadian edition)

$ gcc -std=c11 -pedantic -Wall -Wextra coins.c
$ ./a.out
How many denominations? 6
Enter coin identifier and value in cents: p 1
Enter coin identifier and value in cents: n 5
Enter coin identifier and value in cents: d 10
Enter coin identifier and value in cents: q 25
Enter coin identifier and value in cents: D 100
Enter coin identifier and value in cents: t 200
Enter a command: a t 3
Enter a command: a q 2
Enter a command: s
Identifier,Face Value,Count,Total Value
p,1,0,0
n,5,0,0
d,10,0,0
q,25,2,50
D,100,0,0
t,200,3,600
Overall value of collection: $6.50
Enter a command: q
Bye!

Example 3 (quitting using Control-D)

$ gcc -std=c11 -pedantic -Wall -Wextra coins.c
$ ./a.out
How many denominations? 3
Enter coin identifier and value in cents: A 1 
Enter coin identifier and value in cents: B 13
Enter coin identifier and value in cents: C 51
Enter a command: a B 12
Enter a command: a C 9
Enter a command: s
Identifier,Face Value,Count,Total Value
A,1,0,0
B,13,12,156
C,51,9,459
Overall value of collection: $6.15
Enter a command: [...user types Control-D...]Bye!

Example 4 (user enters invalid number of denominations)

$ gcc -std=c11 -pedantic -Wall -Wextra coins.c
$ ./a.out
How many denominations? foobar
Invalid input

Example 5 (user enters invalid input for coin identifier/value)

$ gcc -std=c11 -pedantic -Wall -Wextra coins.c
$ ./a.out
How many denominations? 3
Enter coin identifier and value in cents: p 1
Enter coin identifier and value in cents: n 5
Enter coin identifier and value in cents: d frotz 
Invalid input

Example 6 (invalid coin identifier)

$ gcc -std=c11 -pedantic -Wall -Wextra coins.c
$ ./a.out
How many denominations? 2
Enter coin identifier and value in cents: p 1
Enter coin identifier and value in cents: n 5
Enter a command: a p 211
Enter a command: a n 19
Enter a command: s
Identifier,Face Value,Count,Total Value
p,1,211,211
n,5,19,95
Overall value of collection: $3.06
Enter a command: a Y 5
Unknown coin identifier

Example 7 (invalid command)

$ gcc -std=c11 -pedantic -Wall -Wextra coins.c
$ ./a.out
How many denominations? 3
Enter coin identifier and value in cents: A 1
Enter coin identifier and value in cents: B 17
Enter coin identifier and value in cents: C 57
Enter a command: a B 13
Enter a command: r B 4
Enter a command: s
Identifier,Face Value,Count,Total Value
A,1,0,0
B,17,9,153
C,57,0,0
Overall value of collection: $1.53
Enter a command: j
Invalid command

Submission

Create a .zip file named hw1.zip which contains only coins.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.

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

• it is not overcommented or undercommented
• there are no ambiguous variable names
• proper/consistent bracket placements and indentation
• no global variables

Two notes regarding automatic checks for programming assignments:

• Passing an automatic check is not itself worth points. (There might be a nominal, low point value like 0.01 associated with a check, but that will not count in the end.) The checks exist to help you and the graders find obvious errors. This will be true for most of the assignments; the actual grades are given manually by the graders, along with comments.
• The automatic checks cover some of the requirements set out in the assignment, but not all. There will be hidden tests that test edge cases. In general, it is up to you to test your own work and ensure your programs satisfy all stated requirements. Passing all the automatic checks does not necessarily mean you will earn all the points.