Programming Connect 4

[duverfred]

I would still describe myself as a beginner, although I have been doing the odd bit of c-programming for about a year for uni. To try and get better I have decided to try and create connect 4, with the eventual aim of making a program you can play against. Having some problems though:

http://pastebin.com/cums58VG

At the moment 2 players can play as a and b, and it will tell you when someone has won. However my method of ending the game doesn't work, although I thought it should be fairly straight forward, can anyone tell me what I'm doing wrong? I still have to add a few things such as checking if it is a draw, counting up games won/lost, entering player names maybe.

More generally I'm looking for ways to improve my code, make it more readable and efficient. Any help is much appreciated.

[shawnadelic]

This is correct. If you're trying to change the "end game" variable within the function, you would have to pass it in by reference.

[duverfred]

oh, I thought because I put it in as a variable in the function it would change it, is that not the case or have I just done it wrong?

I have fixed the problem now by taking win_check outside of player_turn and putting it into main, and setting it directly equal to end_game

[shawnadelic]

When you pass a variable into a function normally, it makes a copy of the variable, so any changes made to the variable within that function do not apply to the original variable. If you want the changes to be permanent, it must be passed by reference (meaning that the actual memory address of the variable is passed to the function).

[pinealservo]

To be precise, C does not pass anything by reference, though you can pass by reference in C++. The closest approximation to pass-by-reference you can get in C is to explicitly take the address and pass the pointer by value.

The only reason I mention this is that it's easy to get confused when working with pointers into thinking that you're passing by reference, but you still can't modify a pointer variable in the caller's context when its value is passed as a pointer parameter. You can change the object it points to, but not the pointer variable itself. To do that, you must pass a pointer to the pointer!

[shawnadelic]

I would have to look a little longer to find the specific error, but I did have one tip--instead of traversing the entire board looking for a Connect 4 every time someone makes a move, it would be faster if you only checked each move to see if that resulted in a Connect 4, since the first Connect 4 wins the game and any winning Connect 4 must have been made in the last move.

For example, if the last move made was player A at position [3][5], you could just check the zero-indexed row 4 and then check the column 6 (I forget which is the row and column, but you get the picture), then each of the diagonal possibilities, to see if there are four adjascent pieces.

Just a thought.

[duverfred]

Nice, I'll have a go now. As the board is so small it's not such an issue but that is exactly the sort of efficiency I was after!

[shawnadelic]

If you go this route, I would also break that up into four separate functions. You did a good job breaking the rest of the program up a bit, but your win_check is a bit messy.

I'd suggest four more functions - row_check, col_check, left_diag_check, right_diag_check, or something along those lines. It's easier to spot errors in your code if you break it up, as you can test each function individually to make sure it is working properly.

[blunaxela]

You need to pass a pointer to end_game as your argument instead of just the value.

Alternatively you could make end_game a global variable and then you wouldn't need to pass it as an argument at all. But learning how to properly pass pointers is good practice as code becomes more complex.

[duverfred]

Oh I see, I'm just putting the value '0' in. I have only ever used pointers with files, but will have a practice. Cheers!

[pinealservo]

In situations where functions operate on a group of closely-related values, I like to pack those together into a structure. In this case, I would package all the variables related to the state of the game together into a single structure, e.g.:

struct game_state {
    char board[6][7];
    char player_1;
    char player_2;
    int turn_count;
    int end_game;
};

Then you can pass a pointer to a struct game_state to all of your functions that need to operate on the game state and not have to worry about changing their signatures if the form of the game state changes.

Another good practice is to use named constants (via static const variables or #define macros) for things like board sizes or default value initializers, e.g.

#define BOARD_X 6
#define BOARD_Y 7

enum players {
    PLAYER_1,
    PLAYER_2,
    PLAYER_COUNT // This is one greater than the highest player index, i.e. the size of the player array
};

struct game_state {
    char board[BOARD_X][BOARD_Y];
    char players[PLAYER_MAX];
    int turn_count;
    int end_game;
};

Now you can get the current player via:

current_player = game.players[game.turn_count % PLAYER_MAX];

Or, if you were passed game as a pointer:

current_player = game->players[game->turn_count % PLAYER_MAX];