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Two Dimensional Arrays

This is a discussion on Two Dimensional Arrays within the C Programming forums, part of the General Programming Boards category; I am very new to C and am getting an error and a warning that I am not sure how ...

  1. #1
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    Two Dimensional Arrays

    I am very new to C and am getting an error and a warning that I am not sure how to fix. I am very prone to problems with declarations and especially the types in declarations so I am fairly sure that is what my problem is. Here is the code:

    Code:
    #include <stdio.h>
    #include <stdlib.h>
    #include <math.h>
    #define BOARD_SIZE 4
    
    void initial_board (char board [], int board_size);
    
    int
    main ()
    {
    
      char board[BOARD_SIZE][BOARD_SIZE];
      initial_board (board, BOARD_SIZE);
    
      return 0;
    }
    
    void
    initial_board (char board [], int board_size)
    {
      int i, j;
      for (i = 0; i < board_size; i++)
        {
          for (j = 0; j < board_size; j++)
        {
          board[i][j] = '.';
        }
        }
      for (i = 0; i < board_size; i++)
        {
          for (j = 0; j < board_size; j++)
        {
          printf ("%\t", board[i][j]);
        }
          printf ("\n");
        }
    }
    What I get when compiling:

    warning: passing argument 1 of "initial_board" from incompatible pointer type.
    occurs at: initial_board (board, BOARD_SIZE);
    note: expected "char *" but argument is of type "char (*)"
    occurs at: oid initial_board (char board [], int board_size);
    error: subscripted value is neither array nor pointer
    occurs at: board[i][j] = '.';
    error: subscripted value is neither array nor pointer
    occurs at: printf ("%\t", board[i][j]);

    Thanks for any help!

  2. #2
    ATH0 quzah's Avatar
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    Why would you think that would work?
    Code:
    void initial_board (char board [], int board_size);
     
    int
    main ()
    {
     
      char board[BOARD_SIZE][BOARD_SIZE];
      initial_board (board, BOARD_SIZE);
    board has 2 dimensions, but your function expects an array that only has one dimension.


    Quzah.
    Hope is the first step on the road to disappointment.

  3. #3
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    Ahh yes, that was quite a silly mistake. However, changing

    Code:
    initial_board (char board[], int board_size)
    to

    Code:
    initial_board (char board[][], int board_size)
    gives me an error of "array type has incomplete element type" even though I want all of the elements of the two dimensional array to be chars.

  4. #4
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    C only allows you have have the leftmost set of brackets empty. You need to put the dimension in the right brackets, like char board[][BOARD_SIZE].

  5. #5
    Here we go again...
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    When passing a multidimensional array in this manner, only the first dimension can be omitted.

    Try:
    Code:
    void initial_board (char board[][BOARD_SIZE], int board_size)
    Also you don't have to pass board_size because you defined it.
    Last edited by rmatze; 10-20-2011 at 04:44 PM. Reason: 30 secs too slow...

  6. #6
    Registered User TheBigH's Avatar
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    The reason for this is that a, say, 50x30 array is stored in memory as 1,500 consecutive elements. If you pass the array to a function, how can the function know it's a 50x30 array and not 30x50 or 15x100 or 3x500 if you don't tell it what the dimensions are?
    rmatze likes this.
    Code:
    while(!asleep) {
       sheep++;
    }

  7. #7
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    Thanks for clearing that up guys. I fixed it and it makes sense. One other quick question that I had though was in terms of returning multiple values. For this program I want to take in a user's input several times and then use that input to manipulate that spot in the array. So I scanf in x and y values for the player's move each turn but how do I return these values from my scanning function so that I can manipulate them in other functions? I know I can't return multiple values, so should I just use pointers for the x and y values and then manipulate them in other functions through the pointers?

  8. #8
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    Yes, you will have to do that with pointers...

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