Lab 3

Logistics

• Due: Friday, September 13th AoE.
• Submission instructions: ensure that you have the source code you want us to grade in a file called lab3.c in your ~/csci112_fall2024/labs/lab3 directory, and that the snapshot (commit) of your repository containing the version of that file you want us to grade has been committed and tagged as lab3. (You should have set up your git repo and practiced tagging a commit in Classwork 4.)

Outside resources

On this assignment, you may not use the the internet or generative AI such as ChatGPT to solicit solutions to the programming part of the assignment. If you are having trouble writing your program, please go to lab (Fridays, 12-4pm in Roberts 111) or post in Slack to get help.

However, you may use those resources for help with navigating the Linux terminal, using vim, and using git, although you may get better answers to your questions by going to lab or posting on Discord anyway.

Learning outcomes

• Practice using if and/or switch statements.
• Practice using functions to organize your code.
• Get input from the user.
• Practice writing complicated output.

Assignment

As a software developer for a chemistry lab, you have been asked to write a program that helps chemists identify a substance given its boiling point. Here is a table of the substances that your lab is interested in, and their boiling points:

Write a program that prompts the user for the observed boiling point of a substance in degrees Celsius, prints the number they entered with only two decimal places, and then prompts them enter a custom error percent. Then, identify the substance if the observed boiling point is within that percent of the expected boiling point. If the data input is outside of range for all of the boiling points in the table, the program should output the message Substance unknown.

For example, if the user selects an error percent of 5%, your program should identify the substance that is within 5% of the expected boiling point. If the data input is more than 5% higher or lower than any of the boiling points in the table, print the above message.

You should use a default percent of 5 if the user does not want to enter a custom percent.

Because your boss anticipates that you and your fellow software engineers will need to write many programs that check whether a given value is inside some range, they have asked that you write and call a specific function that can be reused in other programs.

Your program must define and call a function within_x_percent that takes as a parameter a reference value ref, a data value data, and a percentage value x and returns 1 meaning true if data is within x% of ref — that is, (ref - x% * ref) $\leq$ data $\leq$ (ref + x% * ref). Otherwise within_x_percent should return zero, meaning false. For example, the call within_x_percent(357, 323, 10) would return 1 for true, since 10% of 357 is 35.7, and 323 falls between 321.3 and 392.7. You must use this function to decide what the substance is.

You may optionally start from the starter code in /public/labs/lab3/lab3_starter.c, which gives a skeleton of the program and an example of how you would use within_x_percent to decide whether your observed substance is water.

Example output

[g73x595@csci112 lab3]$ pwd
/home/g73x595/csci112_fall2024/labs/lab3
[g73x595@csci112 lab3]$ gcc -o lab3 -Wall lab3.c
[g73x595@csci112 lab3]$ ./lab3
Observed boiling point (in deg. C)? 101
You entered 101.00
Custom error percent? n for no (5% default), y for yes: n
Substance is water
[g73x595@csci112 lab3]$ ./lab3
Observed boiling point (in deg. C)? 500
You entered 500.00
Custom error percent? n for no (5% default), y for yes: n
Substance unknown
[g73x595@csci112 lab3]$ ./lab3
Observed boiling point (in deg. C)? 400
You entered 400.00
Custom error percent? n for no (5% default), y for yes: y
Enter error percent: 10
You entered 10.00 percent
Substance unknown
[g73x595@csci112 lab3]$ ./lab3
Observed boiling point (in deg. C)? 400
You entered 400.00
Custom error percent? n for no (5% default), y for yes: y
Enter error percent: 15
You entered 15.00 percent
Substance is mercury
[g73x595@csci112 lab3]$ ./lab3
Observed boiling point (in deg. C)? 400
You entered 400.00
Custom error percent? n for no (5% default), y for yes: 15
Error: bad input
[g73x595@csci112 lab3]$ ./lab3
Observed boiling point (in deg. C)? 2200
You entered 2200.00
Custom error percent? n for no (5% default), y for yes: y
Enter error percent: 50
You entered 50.00 percent
Substance is silver

Hints

• If you are having trouble reading in a char, you may need to add a space so that scanf doesn’t consume whitespace from a previous printf. See this stackoverlow post.
• To print a %, use the format %%. For example, printf("5%%") would print 5%.
• Think about what main returns in order to quit the program early.

Grading–100 points

• 5: source file exists with correct name in correct location
• 10: source file compiles
• 5: source file compiles without warnings
• 10: defines function within_x_percent to take in three doubles and return an int
• 10: the function within_x_percent returns 1 if the data value is within percent of the ref value and 0 otherwise
• 10: calls function within_x_percentto decide what the substance is
• 5: the user is prompted to give a custom error percent; if not, uses default of 5%
• 5: accepts n and N for no and y and Y for yes for giving a custom error percent
• 10: for everything else, prints Error: bad input and quits the program
• 5: prompts to user match exactly
• 5: outputs to user match exactly
• 10: prints the correct substance given the temperature and error bound. If multiple match, prints the one with the smaller boiling point.
• 10: prints the message Substance unknown if the entered temperature is not within the given percent of any of the substances’ boiling points.

Autograder

You can run the autograder using

/public/labs/lab3/autograder.sh

A detailed breakdown of your score will be present in autograder.txt.

Grading turnaround

Scores will be uploaded to D2L by class time on Monday, September 16th.