MP 1: Emojis

Due Date: Completed and turned in via git before September 3, 2021 at 11:59pm
Points: MP 1 is worth 50 points


Your first MP in CS 240 is all about getting conformable with memory allocation, pointers, and character encodings in C. You will complete several different sects of functions to build up your C programming skills.

  • You will explore some key differences between C and C++ programs.
  • You will program pointers with various levels of pointer indirection.
  • You will work at the bit- and byte-level to manipulate multi-byte UTF-8 characters in C-strings.
  • You will share with us your favorite emoji! 🎉

Programming Environment

We highly recommend you set up your own computer as your development environment. You will need to be able to program and compile C programs.

To compile your C code:

  • On Windows, you will almost certainly use Windows Subsystem for Linux (WSL) with a Linux distribution like Ubuntu.
  • On Mac OS X, you will almost certainly use the XCode.
  • On Linux, you almost certainly are already ready to go. :)

To edit your C code, you can use your editor of choice. The current popular free editor is Visual Studio Code.

Alterative: Virtual Machine

Alteratively, you have been provided an EngrIT virtual machine (“your CS 240 VM”) for use in CS 240 MPs. The VM is a computer that is entirely yours – you control every bit of the system – and provides you an environment to hack on.

  • You must be connected to the campus VPN to access your CS 240 – VPN install guide.
  • EngrIt has created a “Power On / Reset VM” guide that details how to turn on your CS 240 VM.
  • Your VM will be powered down each day at 5am (unless you’re actively logged in).
  • Once you have powered on your VPN, you can SSH into it with your NetID and password.

Joining @cs240-illinois

If you are not yet part of @cs240-illinois, you will need to be invited to the course:

  1. Go to and either login or create a free account.
  2. On the top-left of the page, you will see your account icon and your username. For example, my username on is wadefagen (this is different than your NetID, unless you set them up as exactly the same).
  3. Fill out this form with your username:
  4. You will have an e-mail back within 24-hours inviting you to join @cs240-illinois and then you can start the MP! :)

Initial Files

Something exciting has happened at Illinois – the University now has an enterprise licence to GitHub, giving us access to all the fanciest of features on “real”!

You will download and turn in your code using the internal CS github server known as github-dev.

  1. Follow our guide to getting your set up.
  2. Once you have your github setup, run the following commands for your cs240/netid/ directory:
    git branch -M main
    git fetch release
    git merge release/mp1 -m "Merging initial files"

Machine Problem

Part 1: Adding Integers

In add_int.c, you will find four functions that require you to add two integers together. Complete each function to return the sum of the two integers provided:

  • In some functions, the integers are provided via an int pointer (int *). You will need to access the contents of the memory pointed to by the pointer to find the integer value. (You may need to review how to dereference a pointer from your C++ course.)

  • In some functions, the function will require you to return your value in newly allocated memory. In C, you can create new memory using the malloc call that will return a pointer to the newly allocated heap memory (similar to the new keyword in C++). To allocate exactly enough memory to store an int, the following code allocates the exact memory required to store an int and stores that in the pointer named result:

int *result = malloc( sizeof(int) );

Running Your Program

We have provided a make file for you to run your code:

  • In your terminal, type make to compile your program.
  • In your terminal, type make test to compile the test suite.
  • Run ./test "[part=1]" to run the tests that have been tagged with [part=1] (covering this portion of the MP).
    • You can call your functions in the main.c file that has been provided for you. Run it with ./main after compiling.
    • You can view/add test cases by viewing the .cpp files in the tests folder.

Part 2: Capitalizing Strings

In capitalizing.c, you will find three functions where you will capitalize one or more letters in a provided string.

  • Remember that strings in C are a pointer (char *) to the beginning of sequence of bytes that ends with a NULL byte (0x00). This means that everything you know about pointers applies here and there is nothing “special” about a string (besides the termination condition).

  • When detecting a lower-case letter, examine an ASCII table to find the range of all possible lower case letters. By using the table, you should also find a way to easily translate any lower-case letter to upper-case. Please do not write 26 if-statements for every possibly letter, you can do it with just math! :)

  • In completing these functions, try to use the earlier functions in your later code. For example, can you call capitalize in capitalizeAll so you do not have to rewrite or copy/paste code?

Testing Part 2

  • In your terminal, type make test to compile the test suite.
  • Run ./test "[part=2]" to run the tests that have been tagged with [part=2].

Part 3: Emojis! 🎉

In emoji.c, you will find your final five functions where you will combine everything you know into working with UTF-8 encoded strings.

  • In emoji_favorite, we just want to know your favorite emoji. You will need to specify a string of bytes that encodes your favorite emoji. In C, you can specify multiple hex-values in a string by using \x followed by two hex digits. For example: "\x45\x67" is the string containing 0x45 (E) and 0x67 (g). Almost all emojis will require four bytes for a single character.

  • For the purpose of this MP, we will consider an emoji to be anything in the inclusive range U+1F000 - U+1FAFF. (There are some invalid characters in this range and a few early emojis outside of this range, but we want to keep it simple. Feel free to be more accurate, we will only test your code on real emoji within this range and your solution won’t break if you program a more correct solution.)

  • In emoji_invertChar, you get to invert an emoji. You must invert “😊” (U+1F60A) to some sort of sad face (your choice!). The inversion is a semantic, so you should invert the meaning of the emoji (not necessarily flipping the bits). In addition to “😊”, you need to invert five other emojis of your choice (and it’s okay to do more than just five).

  • Finally, in emoji_random_alloc, you should generate a new random emoji! The C documentation for rand outlines how to create a random integer in C, which you’ll need to use for your emoji. Make sure that you return a different emoji each time emoji_random_alloc is called.

Running All Three Parts

You can test all three parts of your program together:

  • To compile everything simply run make.
  • To run your code, run ./test and everything should pass! 🎉


When you have completed your program, double-check all three parts run without errors and gets the result your expect. When you are ready, submit the code via the following git commands:

git add -A
git commit -m "MP submission"
git push

You can verify your code was successfully submitted by viewing your git repo on