Strings and Ciphers

Click the orange Accept lab lab03 button at the top of this page, then Accept assignment, wait for the checklist, and click Open repository. Your repository is introduction-to-computer-science-lab03-yourusername.

Still not a member of the organization? Accept the invitation at github.com/FiratUniversity-IJDP-SoftEng first; the setup guide has the details.

Green Code button → Codespaces → Create codespace on main. When the terminal shows a $ prompt:

$ python3 check.py:| scores.c: 72, 73, 33 → Min 33, Max 73, Average 59.33
  got 'How many scores? Score: Score: Score: '
...
0/17 checks passed

Ask how many scores there are (1 to 10, re-prompt otherwise), read that many integers into an array, and print the minimum, the maximum and the average with two decimals:

$ make scores$ ./scoresHow many scores? 3
Score: 72
Score: 73
Score: 33
Min: 33
Max: 73
Average: 59.33

The three functions are declared for you: lowest, highest and average, each taking the length and the array, exactly like average(int length, int array[]) in the lecture’s scores5.c. Fill them in, then complete main.

Two things to notice. First, int scores[n]; after reading n is allowed in C: the size does not have to be a constant. Second, the smallest value in an array is found by assuming the first element is the smallest and then letting every other element challenge it; the same with the largest.

Read a text and print the U.S. school grade needed to read it, with the Coleman–Liau index:

index = 0.0588 × L − 0.296 × S − 15.8

where L is the average number of letters per 100 words and S the average number of sentences per 100 words. Round the index to the nearest whole number; print Before Grade 1 if it is below 1, Grade 16+ if it is 16 or more, otherwise Grade N.

$ make readability$ ./readabilityText: Congratulations! Today is your day. You're off to Great Places! You're off and away!
Grade 3

Counting rules, the same as CS50’s: a letter is anything for which isalpha is true; words are separated by single spaces, so the number of words is the number of spaces plus one; a sentence ends with ., ! or ?. Write the three counting functions first and test each with a printf before you compute the index. For the example above you should count 65 letters, 14 words and 4 sentences.

A Caesar cipher whose key comes from the command line:

$ make caesar$ ./caesar 13plaintext:  HELLO, world
ciphertext: URYYB, jbeyq

The rules, in the order you should implement them:

1. Validate. Exactly one argument, made only of digits. Otherwise print Usage: ./caesar key and return 1. only_digits is declared for you; isdigit from <ctype.h> checks one character. Test it before anything else: ./caesar, ./caesar 1 2, ./caesar abc must all print the usage line, and echo $? must show 1.
2. Convert the key with atoi(argv[1]) from <stdlib.h>.
3. Read the plaintext with get_string("plaintext: "), print ciphertext: , then every character passed through rotate.
4. Rotate. An uppercase letter’s position is c - 'A'; add the key, take % 26, add 'A' back. The same with 'a' for lowercase. Anything that is not a letter is returned unchanged. Keys larger than 26 must work; % 26 takes care of that.

$ ./caesar 3$ ./caesar 27plaintext:  xyz XYZ
ciphertext: abc ABC
plaintext:  abc
ciphertext: bcd

Encrypt something with 13, then encrypt the result with 13 again. You get the original back; ROT13 is its own inverse, and the notebook below shows why.

When python3 check.py is green (or when you have done what you can):

$ git add -A$ git commit -m "Lab 3"$ git push

About two minutes later your score appears under Releases in your repository and on classroom50.org. Push as often as you like before Friday, October 16, 23:59; the last push before the deadline counts, and late pushes lose 10% per day for up to five days.