The Game of Connect 4

Connect 4, or 4 in a Line, is a simple board game played for centuries around the world. Legend has it that Captain Cook would disappear to his quarters for extended periods of time to play the game. When the crew discovered his preoccupation, they nicknamed the game "The Captain's Mistress"!

Connect-4 is a two-person game. The game involves the two players alternating turns. It consists of a grid with columns and rows as shown in Figure below. At his/her turn, a player drops a checker into the column of his/her choice. The game play continues until one of the players gets 4 checkers in a line. The line can be horizontal, vertical, or diagonal.

This assignment requires you to implement a Connect-4 game in LC-3. The game will interact with the two players via the console and the keyboard.

  1. Rules

    In our variation of Connect 4, the game board consists of a 6 by 6 grid.

    The rules are as follows:

  2. What to do

    At the beginning of the game you should display the initial state of the game board. You should use the ASCII character "-" (ASCII code x002D) to represent an empty location in the grid, "O" (ASCII code x004F) to represent a checker of Player 1, and "X" (ASCII code x0058) to represent a checker of Player 2. To make your grid easier to read, output a space BETWEEN each column. Do not output a space after the 6th column. The initial state of the game board should look as follows:

    - - - - - -
    - - - - - -
    - - - - - -
    - - - - - -
    - - - - - -
    - - - - - -

    Player 1 always goes first, and play alternates between Player 1 and Player 2. At the beginning of each turn you should output which player's turn it is, and prompt the player for her move. For Player 1 this should look as follows:

        Player 1, choose a column:

    To specify which column to drop a checker into, the player should input a single digit from 1 to 6, followed by pressing ENTER. The number (from 1 to 6) specifies which column is selected, from left to right. For example, if the player wants to drop a checker into the 2nd column from the left, they would type 2 and then press enter. Your program must make sure the player's input referred to a valid column. If the player's move is invalid, you should output an error message and prompt the same player for a move. For example, if it is Player 1's turn:

        Player 1, choose a column: D
        Invalid move. Try again.
        Player 1, choose a column: 7
        Invalid move. Try again.
        Player 1, choose a column:

    Note that you should output the same invalid move message if the player tries to play in a column which is already full.

    Your program should keep prompting the player until a valid move is chosen. Be sure your program echoes the player's move to the screen as they type it. After you have echoed the player's move, you should output a newline character (ASCII code x000A) to move the cursor to the next line.

    After a player has chosen a valid move, you should update the state of the game board to reflect the move, re-display the updated game board, and check for a winner. If there is no winner, you should continue with the next player's turn.

    When a player has won or a tie has occurred, the game is over. At this point, your program should show the final board and then halt. For example, if Player 2 has four adjacent checkers, your program should output the following:

        Player 2 Wins.

    If a tie occurs, your program should output the following:

        Tie Game.

  3. Sample Input/Output

    An example of the input/output for a game being played can be found here. To receive full credit for your program, your input/output format MUST EXACTLY MATCH the format in the example.

  4. Hints and Suggestions

    One implementation is to allocate 36 locations in memory to represent each location on the grid. To make traversal of the grid easiest, you could store 0 if the location is empty, 1 if the location is occupied by Player 1, and -1 if the location is occupied by Player 2. The goal is to make maximal use of condition codes.

    Remember, all input and output functions use ASCII characters. You are responsible for making any conversions that are necessary.

    For character input from the keyboard in this assignment, you should use TRAP x20 (GETC). To echo the characters onto the screen, you should follow each TRAP x20 with a TRAP x21 (OUT). Recall that TRAP x23 displays a banner to prompt the person at the keyboard to input a character. You do not need that banner since your program has its own style of prompt. Therefore you should use TRAP x20 which does the same as TRAP x23 except it does not print a banner on the screen to prompt for input.

    You should use subroutines where appropriate.

    In each subroutine you write, you should save and restore any registers that you use. This will avoid a major headache during debugging.

  5. Notes: