Project 1: snek

Deadline: Wednesday, February 9, 11:59:59 PM PT

Welcome to the first project of 61C! In this project, you'll get some practice with C coding by creating a playable snake game. If you're not familiar with snake, you can try out a demo at this link.

Content in scope for this project: Lectures 2-4, Discussion 2, Labs 1-2, and Homework 2. Also, make sure you've finished the setup in Lab 0.

Setup

This assignment can be done alone or with a partner. Once you run these steps, you will not be able to change (add, remove, or swap) partners for this project, so please be sure of your partner before starting the project. If there are extenuating circumstances that require a partner switch (e.g. your partner drops the class, your partner is unresponsive), please reach out to us privately.

  1. Visit Galloc. Log in and start the Project 1 assignment. This will create a GitHub repository for your work. If you have a partner, one partner should create a repo and invite the other partner to that repo. The other partner should accept the invite without creating their own repo.

  2. Clone the repository on your workspace. We recommend using the hive machines.

    git clone git@github.com:61c-student/sp22-proj1-USERNAME.git 61c-proj1

    (replace USERNAME with your GitHub username)

  3. Navigate to your repository:

    cd 61c-proj1

  4. Add the starter repository as a remote:

    git remote add starter https://github.com/61c-teach/sp22-proj1-starter.git

Conceptual Overview

The game board

A snake game can be represented by a rectangular grid of characters. The grid contains walls, fruits, and one or more snakes. An example of a game is shown below:

##############
#            #
#    dv      #
#     v   #  #
#     v   #  #
#   s >>> #  #
#   v     #  #
# *<<  *  #  #
#            #
##############

The grid has the following special characters:

  • # denotes a wall.
  • (space character) denotes an empty space.
  • * denotes a fruit.
  • wasd denotes the tail of a snake.
  • ^<v> denotes the body of a snake.
  • x denotes the head of a snake that has died.

Each character of the snake tells you what direction the snake is currently heading in:

  • w or ^ denotes up
  • a or < denotes left
  • s or v denotes down
  • d or > denotes right

At each time step, each snakes moves according to the following rules:

  • Each snake moves one step in the direction of its head.
  • If the head crashes into the body of a snake or a wall, the snake dies and stops moving. When a snake dies, the head is replaced with an x.
  • If the head moves into a fruit, the snake eats the fruit and grows by 1 unit in length. Each time fruit is consumed, a new fruit is generated on the board.

In the example above, after one time step, the board will look like this:

##############
#         *  #
#     s      #
#     v   #  #
#     v   #  #
#   s >>>>#  #
#   v     #  #
# <<<  *  #  #
#            #
##############

After one more time step, the board will look like this:

##############
#         *  #
#     s      #
#     v   #  #
#     v   #  #
#     >>>x#  #
#   s     #  #
#<<<<  *  #  #
#            #
##############

Numbering snakes

Each snake on the board is numbered depending on the position of its tail, in the order that the tails appear in the file (going from top-to-bottom, then left-to-right). For example, consider the following board with four snakes:

#############
#  s  d>>>  #
#  v   <<a  #
#  v        #
#       ^   #
#       w   #
#############

Snake 0 is the snake with tail s, snake 1 has tail d, snake 2 has tail a, and snake 3 has tail w.

Once the snakes are numbered from their initial positions, the numbering of the snakes does not change throughout the game.

The game_state_t struct

A snake game is stored in memory in a game_state_t struct. The struct contains the following fields:

  • unsigned int x_size: Width of the game board.
  • unsigned int y_size: Height of the game board.
  • char** board: The game board in memory. Each element of the board array is a char* pointer to a character array containing a row of the map.
  • unsigned int num_snakes: The number of snakes on the board.
  • snake* snakes: An array of snake structs.

The snake struct

Each snake struct contains the following fields:

  • unsigned int tail_x: The x-coordinate (column) of the snake's tail.
  • unsigned int tail_y: The y-coordinate (row) of the snake's tail.
  • unsigned int head_x: The x-coordinate (column) of the snake's head.
  • unsigned int head_y: The y-coordinate (row) of the snake's head.
  • bool live: true if the snake is alive, and false if the snake is dead.

Please don't modify the provided struct definitions. You should only need to modify state.c and snake.c in this project.

Task 1: create_default_state

Implement the create_default_state function in state.c. This function should create a default snake game in memory with the following starting state (which you can hardcode), and return a pointer to the newly created game_state_t struct.

##############
#            #
#        *   #
#            #
#   d>       #
#            #
#            #
#            #
#            #
##############
create_default_state
Arguments None
Return values game_state_t * A pointer to the newly created game_state_t struct.

Hints

  • The board has 10 rows and 14 columns. The fruit is at row 2, column 9 (zero-indexed). The tail is at row 4, column 4, and the head is at row 4, column 5.
  • Which part of memory (code, static, stack, heap) should you store the new game in?
  • strcpy may be helpful.

Testing and debugging

You can run make run-unit-tests to check your implementation for each task. Please note that the unit tests are not comprehensive, and passing them does not guarantee that your implementation is fully correct. However, they should be helpful to get you started with debugging.

If your implementation isn't working, it's time to start debugging. You can add printf statements in your code to print out variables during code execution, and then run make run-unit-tests again to see the output of your print statements.

Also, you can use make debug-unit-tests to start CGDB.

Task 2: free_state

Implement the free_state function in state.c. This function should free all memory allocated for the given state, including all snake structs and all map contents.

free_state
Arguments game_state_t* state A pointer to the game_state_t struct to be freed
Return values None

Testing and debugging

To test if we correctly freed memory for the game state, run make valgrind-unit-tests to check for memory leaks. If nothing is leaked, then you've passed the unit test for this task.

Task 3: print_board

Implement the print_board function in state.c. This function should print out the given game board to the given file pointer.

print_board
Arguments game_state_t* state A pointer to the game_state_t struct to be printed
FILE* fp A pointer to the file object where the board should be printed to
Return values None

Hints

  • The fprintf function will help you print out characters and/or strings to a given file pointer.

Testing and debugging

Run make run-unit-tests and make debug-unit-tests to test and debug, just like before. Remember to uncomment out the lines you commented out from the previous task before running tests.

If your function executes successfully (doesn't segfault or crash) but doesn't print the correct output, the board you printed will be in unit-test-out.snk. A correctly-printed board should match the default board from Task 1.

Task 4: update_state

Implement the update_state function in state.c. This function should move the snakes one timestep according to the rules of the game.

You are free to implement this function however you want, but you'd like, you can work through this task by implementing the helper functions we've provided. Helper functions are not graded; for this task, we'll only be checking that update_state is correct.

Task 4.1: Helpers

We have provided the following helper function definitions that you can implement. These functions are entirely independent of any game board or snake; they only take in a single character and output some information about that character.

  • bool is_tail(char c): Returns true if c is part of the snake's tail. The snake's tail consists of these characters: wasd. Returns false otherwise.
  • bool is_snake(char c): Returns true if c is part of the snake. The snake consists of these characters: wasd^<>vx. Returns false otherwise.
  • char body_to_tail(char c): Converts a character in the snake's body (^<>v) to the matching character representing the snake's tail (wasd).
  • int incr_x(char c): Returns 1 if c is > or d. Returns -1 if c is < or a. Returns 0 otherwise.
  • int incr_y(char c): Returns 1 if c is v or s. Returns -1 if c is ^ or w. Returns 0 otherwise.

Unit tests are not provided for these helper functions, but we encourage you to write your own tests to make sure that these are working as expected! You can modify test_is_tail, test_is_snake, test_body_to_tail, test_incr_x, and test_incr_y in unit-tests.c to write your own unit tests.

When writing a unit test, the test function should return false if the test fails, and true if the test passes. You can use printf to print out debugging statements. assert_equals_char might be a helpful function to use for these tests.

Once you've written your own unit tests, you can run them with make run-unit-tests and make debug-unit-tests as usual.

Task 4.2: next_square

Implement the next_square helper function in state.c. This function returns the character in the cell the given snake is moving into. This function should not modify anything in the game stored in memory.

next_square
Arguments game_state_t* state A pointer to the game_state_t struct to be analyzed
int snum The index of the snake to be analyzed
Return values char The character in the cell the given snake is moving into

As an example, consider the following board:

##############
#            #
#        *   #
#            #
#   d>x      #
#            #
#       s    #
#       v    #
#       v    #
##############

Assuming that state is a pointer to this game state, then next_square(state, 0) should return x, because the head of snake 0 is moving into a cell with x in it. Similarly, next_square(state, 1) should return # for snake 1.

The helper functions you wrote earlier might be helpful for this function (and the rest of this task too). Also, check out get_board_at and set_board_at, which are helper functions we wrote for you.

Use make run-unit-tests and make debug-unit-tests to run the provided unit tests.

Task 4.3: update_head

Implement the update_head function in state.c. This function will update the head of the snake.

Remember that you will need to update the head both on the game board and in the snake struct. On the game board, add a character where the snake is moving. In the snake struct, update the x and y coordinates of the head.

update_head
Arguments game_state_t* state A pointer to the game_state_t struct to be updated
int snum The index of the snake to be updated
Return values None

As an example, consider the following board:

##############
#   d>>      #
#        *   #
#        ^   #
#        ^   #
#        ^   #
#        w   #
#            #
#            #
##############

Assuming that state is a pointer to this game state, then update_head(state, 0) will move the head of snake 0, leaving all other snakes unchanged. In the snake_t struct corresponding to snake 0, the head_x value should be updated from 6 to 7, and the head_y value should stay unchanged at 1. The new board will look like this:

##############
#   d>>>     #
#        *   #
#        ^   #
#        ^   #
#        ^   #
#        w   #
#            #
#            #
##############

Note that this function ignores food, walls, and snake bodies when moving the head.

Use make run-unit-tests and make debug-unit-tests to run the provided unit tests.

Task 4.4: update_tail

Implement the update_tail function in state.c. This function will update the tail of the snake.

Remember that you will need to update the tail both on the game board and in the snake struct. On the game board, blank out the current tail, and change the new tail from a body character (^v<>) into a tail character (wasd). In the snake struct, update the x and y coordinates of the tail.

update_tail
Arguments game_state_t* state A pointer to the game_state_t struct to be updated
int snum The index of the snake to be updated
Return values None

As an example, consider the following board:

##############
#   d>>      #
#        *   #
#        ^   #
#        ^   #
#        ^   #
#        w   #
#            #
#            #
##############

Assuming that state is a pointer to this game state, then update_tail(state, 1) will move the tail of snake 1, leaving all other snakes unchanged. In the snake_t struct corresponding to snake 1, the tail_y value should be updated from 6 to 5, and the tail_x value should stay unchanged at 9. The new board will look like this:

##############
#   d>>      #
#        *   #
#        ^   #
#        ^   #
#        w   #
#            #
#            #
#            #
##############

Use make run-unit-tests and make debug-unit-tests to run the provided unit tests.

Task 4.5: update_state

Using the helpers you created, implement update_state in state.c.

As a reminder, the rules for moving a snake are as follows:

  • Each snake moves one step in the direction of its head.
  • If the head crashes into the body of a snake or a wall, the snake dies and stops moving. When a snake dies, the head is replaced with an x.
  • If the head moves into a fruit, the snake eats the fruit and grows by 1 unit in length. (You can implement growing by 1 unit by updating the head without updating the tail.) Each time fruit is consumed, a new fruit is generated on the board.

The int (*add_food)(game_state_t* state) argument is a function pointer, which means that add_food is a pointer to the code section of memory. The code that add_food is pointing at is a function that takes in game_state_t* state as an argument and returns an int. You can call this function with add_food(x), replacing x with your argument, to add a fruit to the board.

update_state
Arguments game_state_t* state A pointer to the game_state_t struct to be updated
int (*add_food)(game_state_t* state) A pointer to a function that will add fruit to the board
Return values None

Use make run-unit-tests and make debug-unit-tests to run the provided unit tests.

Task 5: load_board

Implement the load_board function in state.c. This function will read a game board from a file into memory.

The game board can be of any size, but you may assume that the board is shaped like a rectangle (each row is the same length), with walls on all four sides.

Tasks 5 and 6 combined will create a game_state_t struct in memory with all its fields set up. In this task, you can leave num_snakes and the snakes array uninitialized, as long as x_size, y_size, and board are correctly set up.

load_board
Arguments char* filename The name of the file where the board is stored
Return values game_state_t * A pointer to the newly created game_state_t struct.

Use make run-unit-tests and make debug-unit-tests to run the provided unit tests.

Task 6: initialize_snake

Implement the initialize_snake function in state.c. This function takes in a game board and creates the array of snake structs.

You are free to implement this function however you want, but you'd like, you can work through this task by implementing the helper function we've provided.

Task 6.1: find_head

Implement the find_head function in state.c. Given a snake struct with the tail coordinates filled in, this function traces through the board to find the head coordinates, and fills in the head coordinates in the struct.

find_head
Arguments game_state_t* state A pointer to the game_state_t struct to be analyzed
int snum The index of the snake to be analyzed
Return values None

As an example, consider the following board:

##############
#            #
#        *   #
#            #
#   d>v      #
#     v      #
#  ^  v      #
#  ^<<<      #
#            #
##############

Assuming that state is a pointer to this game state, then find_head(state, 0) will fill in the head_x and head_y fields of the snake 0 struct with 3 and 6, respectively.

Use make run-unit-tests and make debug-unit-tests to run the provided unit tests.

Task 6.2: initialize_snake

Using find_head, implement the initialize_snake function in state.c. You can assume that the state passed into this function is the result of calling load_board. This means the board-related fields are already filled in, and you only need to fill in num_snakes and create the snakes array.

You may assume that all snakes on the board start out alive.

initialize_snakes
Arguments game_state_t* state A pointer to the game_state_t struct to be filled in
Return values game_state_t* state A pointer to the game_state_t struct with fields filled in. This can be the same as the struct passed in (you can modify the struct in-place).

Use make run-unit-tests and make debug-unit-tests to run the provided unit tests.

Task 7: main

Using the functions you implemented in all the previous tasks, fill in the blanks in snake.c. Each time the snake.c program is run, the board will be updated by one time step.

To test your full implementation, run make run-integration-tests.

To debug your implementation, run cgdb --args ./snake -i tests/TESTNAME-in.snk -o tests/TESTNAME-out.snk, replacing TESTNAME with one of the test names in the tests folder:

  • 1-simple
  • 2-direction
  • 3-tail
  • 4-food
  • 5-wall
  • 6-small
  • 7-large
  • 8-multisnake
  • 9-everything

Task 8: README

Congratulations on finishing the project! This is a brand-new project, so we'd love to hear your feedback on what can be improved for future semesters. Fill in README.md with your thoughts about the project: how long did each task take you? What were some bugs you encountered? What was the hardest/easiest/most fun/least fun part of the project? Anything you'd like to say about the project is fair game here, but 512 characters minimum, please!

Submission and Grading

Submit your code to the Gradescope assignment. Make sure that you have only modified snake.c and state.c. The score you see on Gradescope will be your final score for this project.

Just for fun: play snake

Now you can play a game with the code you've written by make interactive-snake followed by ./interactive-snake. To speed up the game, you can run ./interactive-snake -d 0.5 (replacing 0.5 with the number of seconds between time steps).