If you haven't already, make sure you get your CS Unix account and test your programs there!

• Readings: C text Chapters 1-5, Appendices A & B. Much of this material (Chapters 2 & 3 in particular) will be familiar to you already.
• Tutorials: Using Unix, an editor of your choice (emacs or vi) - do some web searches in addition to what is posted and linked to.
• Compilation: gcc -ansi -std=c99 -pedantic -Wall -Wextra -O pg#.c
• Submission: Name your source file with main pg1.c. Upload all source files (*.c) for a particular assignment part to that webCT assignment page. Make sure that you hit SUBMIT after uploading. You can retrieve and resubmit as many times as you want before the deadline. If you retrieve, it's as if you never submitted, so make sure you have time to resubmit! If you need to explain anything in general, include a README plain text file with your submission. Anything not on webCT by the deadline gets a 0 = no credit. Also bring a printout of your source code to class on the due date.
• Collaboration: This is an individual assignment. Remember that you may use or adapt code from your texts and lectures, but you MUST include a comment to cite the original source.
• Help: check the TA info course webpage for hours when help will be available in the CS lab. This will be updated through the next week as the schedule gets set up.
• Grading: 5 points style & submission, 25 points functionality = 30 total. -5 points if there are any warnings using the required compilation options. 0 points if it doesn't compile (has errors, no a.out created).

The Problem: Simple Encryption

Write a program that uses the bit operators to perform two different forms of simple encryption on a single line of plain text input. In both forms, you will be applying transformations to individual characters in the text. For the purpose of this assignment, you may assume that no line of input contains more than 80 characters. (Make sure that the 80 limit is something that can be changed easily within your program.)

The first type of transformation is to perform a one's complement of each non-space character using the ~ bit operator. All whitespace characters should remain intact. Then display the message using whatever characters result from the bit transformation. The cool thing about this particular encryption is that in order to decrypt a message you perform the same operation. It is its own inverse.

The second type of transformation is to perform a left bit shift to encrypt each character, including any whitespace. The shift value must be an integer which is less than the number of bits in a char variable. Prompt the user to enter this value, given an appropriate range. Do error checking on this input. However, you will need to store the characters in an integer data type that is twice as large as the character type in order to not lose significant bits when shifting. (Use the sizeof function to determine exactly which data type is most appropriate, and consider using a unsigned type for the best results.) With this transformation, you must display the encrypted values as integers, not as characters, separated by spaces. In order to decrypt this type of message, simply do a right bit shift using the same shift value.

The overall operation of your program should be as follows:

• Read a single line of text input.
• Display the input in it's character form.
• Display the one's complement encryption in character form.
• Display the decrypted one's complement.
• Get the shift value from the user (error check until valid).
• Display the input in it's integer (ASCII value) form.
• Display the left shift encrypted form of the input.
• Display the right shift decrypted result.

You must have at least three functions in your program: 1) create the one's complement of a character array, 2) encrypt a message using a left shift, 3) decrypt a message using a right shift. It is up to you to determine what parameter types and return values (if any) work best for these methods. Use other functions in your program to make the most of code reuse and good structured programming. You must not use any global variables.