Skip to main content Link Search Menu Expand Document (external link)
COMP251

Programming Kata 2

Change your working directory to your portfolio and create a new branch for this assignment.

$ cd <your-portfolio-directory>
$ git checkout -b <your-branch-name>

Now, create a subdirectory for this exercise and change your working directory to inside it.

$ mkdir exercise02
$ cd exercise02

Now create your C file and start coding!

$ vim cipher.c

Assignment

Write a program that accepts a 26-character string that represents a substitution cipher.

For example, if the input is qwertyuiopasdfghjklzxcvbnm, then the letter a will be replaced by q, b with w, c with e, etc.

Your program should then enter a loop to encipher/decipher text.

$ gcc cipher.c -o cipher
$ ./cipher
Enter substitution pad: qwertyuiopasdfghjklzxcvbnm
hello world! this is plaintext -- let's see it in ciphertext!
itssg vgksr! ziol ol hsqofztbz -- stz'l ltt oz of eohitkztbz!
this is another test. The encipher/decipher does not need to USE CAPITAL LETTERS
or punctuation...they can be ignored.
ziol ol qfgzitk ztlz. Tit tfeohitk/rteohitk rgtl fgz fttr zg USE CAPITAL LETTERS
gk hxfezxqzogf...zitn eqf wt oufgktr.
^C

Tips

  • You can assume that the text that the user enters is less than 1024 characters.
  • char is an integer type, and characters are represented as numeric values internally. A common encoding of basic characters used in English is ASCII.
  • You can use this by performing arithmetic and comparison between characters in strings and letters. (e.g., str[i] >= 'a' evaluates to true if the character at position i is a letter “greater than” a).
  • You can also perform arithmetic with characters: 'd' - 2 evaulates to b, for example. Likewise 'd' - 'a' evaluates to 4.

Turning it in

When you are complete, commit your code and create a pull request with your exercise.

Change to the root directory of your repository:

$ cd ..

Add a line to the .gitignore file to exclude your binary.

$ echo exercise02/cipher >> .gitignore

Add the new directory (and file) to your staged commit and verify your files are staged.

$ git add exercise02
$ git status

Commit your code and push it to GitHub!

$ git commit -m "<your commit message>"
$ git push -u origin <your-branch>

There will be a link to create a pull request in the upload message. Click the link and create a PR. Add me as reviewer.