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Passing a int[ ][ ] to a function

This is a discussion on Passing a int[ ][ ] to a function within the C Programming forums, part of the General Programming Boards category; I looked online and did what they said, but something isn't right. I put "void seatChart (int AvailableSeats[][]);" which won't ...

  1. #1
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    Passing a int[ ][ ] to a function

    I looked online and did what they said, but something isn't right. I put
    "void seatChart (int AvailableSeats[][]);" which won't compile. I even put [14][19] in the braces which would compile then but quit on me as soon as it reaches a reference to AvailableSeats[x][y].

    What am I doing wrong? Thanks yet again!

    Code:
    #include <stdio.h>
    #include <stdlib.h>
    
    void seatChart (int AvailableSeats[][]);
    
    int main()
    {
        float sale;
    
        int choice;
    
        int row;
        int seat;
    
        int AvailableSeats[14][19] = {0}; //seats[row][seat]
    
    
    
    
        for(;;)
        {
            seatChart(AvailableSeats[14][19]);
    
            printf("\n\nMenu:");
            printf("\n1) Buy ticket");
            printf("\n2)Total sell and exit");
            printf("\n\nEnter your choice : ");
            scanf("%d", &choice);
    
            if (choice == 1)
            {
                printf("\n\nEnter row: ");
                scanf("%d", &row);
    
                printf("\nEnter seat: ");
                scanf("%d", &seat);
    
                AvailableSeats[row][seat] = 1;
    
                continue;
            }
    
            if(choice == 2)
            {
                printf("\n\nTOTAL TICKETS SOLD: X");
                printf("\nTOTAL REVENUE: Y");
                break;
            }
    
            printf("Invalid choice");
    
        }
    
    
        return 0;
    }
    
    void seatChart (int AvailableSeats[][])
    {
        int i;
        int o;
    
        printf("\n* Seats available");
        printf("\n# Reserved Seats");
        printf("\nSeats:  0  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19");
    
    
    
        for(o = 0; o<=14; o++)
        {
            printf("\nRow %2d", o);
    
            for(i = 0; i<=19; i++)
            {
                if(AvailableSeats[o][i]==0)
                {
                    printf("  *");
                }
                if(AvailableSeats[o][i]==1)
                {
                    printf("  #");
                }
            }
        }
    
    }
    My Ctrl+S addiction gets in the way when using Code Blocks...

  2. #2
    - - - - - - - - oogabooga's Avatar
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    At a minimum, you must specify all but the leftmost dimension, and you can specify the leftmost dimension also.
    Code:
    void seatChart (int AvailableSeats[][19])
    Usually you would #define such constants so they can be easily changed and are better documented.

    Also, in your loop you are going up to <= the dimensions, but it should just be <, otherwise you go one-to-far.
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  3. #3
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    Also, when calling it, use
    Code:
       seatChart(AvailableSeats);
    not
    Code:
       seatChart(AvailableSeats[14][19]);
    The first passes an array (which is what the function expects). The second form passes a single integer value (which is not what the function is written to expect).
    Right 98% of the time, and don't care about the other 3%.

  4. #4
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    ah, stupid of me, thanks!

    Edit: Thanks both of you! Two problems solved and program is working as expected Much appreciated!
    Last edited by JonathanS; 01-23-2012 at 11:53 PM.
    My Ctrl+S addiction gets in the way when using Code Blocks...

  5. #5
    msh
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    Code:
    void seatChart(int *AvailableSeats, int h, int w);
    
    int main(void)
    {
            const int h = 14;
            const int w = 18;
            int AvailableSeats[h][w] = {0};
            /*...*/
            while(1) {
                    seatChart(AvailableSeats, h, w);
                    /*...*/
            }
            return 0;
    }
    
    void seatChart(int *AvailableSeats, int h, int w)
    {
            /*...*/
            int i, t;
            for (i = 0; i < h; ++i) {
                    /*...*/
                    for (t = 0; t < w; ++t) {
                            /*...*/
                    }
            }
    }
    Don't overthink this. `AvailableSeats` is just a contiguous block of memory with a size `sizeof(int) * h * w`. Pass a pointer to the start of the block and its dimensions. Then use these dimensions as limits for indexing into it.

    `for(; ;)` is old-school and unnecessary. I hear is ye olde days compilers could optimize it better or something, but that's on longer true and the current idiom for infinite loop that will be manually broken out of is `while (1)`.
    Disclaimer: This post shows my ignorance at the time of its making. I claim ownership of but not responsibility for all errors in it. Reference at your own peril.

  6. #6
    C++ Witch laserlight's Avatar
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    Quote Originally Posted by msh
    `AvailableSeats` is just a contiguous block of memory with a size `sizeof(int) * h * w`. Pass a pointer to the start of the block and its dimensions. Then use these dimensions as limits for indexing into it.
    If you want to use msh's suggestion, then the correct way to call the function is:
    Code:
    seatChart(&AvailableSeats[0][0], h, w);
    Quote Originally Posted by msh
    `for(; ;)` is old-school and unnecessary. I hear is ye olde days compilers could optimize it better or something, but that's on longer true and the current idiom for infinite loop that will be manually broken out of is `while (1)`.
    I think for(;;) is canonical and fine.
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  7. #7
    msh
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    Quote Originally Posted by laserlight View Post
    If you want to use msh's suggestion, then the correct way to call the function is:
    Code:
    seatChart(&AvailableSeats[0][0], h, w);
    Thanks for the catch. :)

    Quote Originally Posted by laserlight View Post
    I think for(;;) is canonical and fine.
    I find it ugly and obscure.
    Disclaimer: This post shows my ignorance at the time of its making. I claim ownership of but not responsibility for all errors in it. Reference at your own peril.

  8. #8
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    If you are seeking an infinite loop, whatever works and is understandable is fine. Any preferences are stylistic, not technical.

    Given that the OP is using a break statement to end the "infinite" loop, I would generally prefer to do something like "int continuing = 1; while (continuing) .... " and set continuing to zero when done - rather than using break or continue statements.

    Incidentally, it still amuses me that folks in the "goto is evil" religion often make use of break or continue statements to break out or skip parts of infinite loops.... effectively, that is using them as closet goto statements.

    If it walks like a duck and quacks like a duck, then it is a good bet it is actually a duck.
    Right 98% of the time, and don't care about the other 3%.

  9. #9
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    Quote Originally Posted by laserlight View Post
    If you want to use msh's suggestion, then the correct way to call the function is:
    Code:
    seatChart(&AvailableSeats[0][0], h, w);

    I thought it was:
    Code:
    seatChart(h,w,AvailableSeats)
    
    void ( int h, int w, int seatChart[h][w]){...}   //VLA

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