Pointer Syntax

This is a discussion on Pointer Syntax within the C Programming forums, part of the General Programming Boards category; I've got a card dealing program and I want to convert all the array syntax into pointer syntax. Whereas in ...

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    Question Pointer Syntax

    I've got a card dealing program and I want to convert all the array syntax into pointer syntax. Whereas in array syntax I would just use the element's subscript (i.e. arr[3] ) in pointer syntax I need to use the address of the first element and add to it the number of bytes of memory I want to move over (i.e. *(arr+3) ). I know this is the long way around but I need a way to do this for a multi-dimensional array.




    How can I turn this into pointer syntax?

    wDeck[row][column]
    don't be a two-bit user

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    End Of Line Hammer's Avatar
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    Here's some good reading for you to get started with...
    When all else fails, read the instructions.
    If you're posting code, use code tags: [code] /* insert code here */ [/code]

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    Confused Magos's Avatar
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    Array[X + (Y * MaxX)]

    X = column
    Y = row
    MaxX = Maximum number of columns available
    MagosX.com

    Give a man a fish and you feed him for a day.
    Teach a man to fish and you feed him for a lifetime.

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    Thank You Magos! I knew that formula existed I just couldn't figure it out. Again thanks!
    don't be a two-bit user

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    moi
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    Originally posted by Magos
    Array[X + (Y * MaxX)]

    X = column
    Y = row
    MaxX = Maximum number of columns available
    /me winces

    did you try compiling this? didn't think so. used with his array wDeck[row][column], this yields a pointer to an integer (NOT an integer) that is out-of-bounds (i.e. not in your memory area). the real answer is here.

    and if you're curious, i wasn't 100% sure about my answer either, so i tried compiling it and guess what? it worked.

    edit: btw i don't expect anyone to try a test compile before they answer every question, but if you're not quite sure wth you are doing, then, yeah.
    Last edited by moi; 09-12-2002 at 06:21 PM.
    hello, internet!

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    Confused Magos's Avatar
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    Originally posted by moi
    /me winces

    did you try compiling this? didn't think so. used with his array wDeck[row][column], this yields a pointer to an integer (NOT an integer) that is out-of-bounds (i.e. not in your memory area). the real answer is here.

    and if you're curious, i wasn't 100% sure about my answer either, so i tried compiling it and guess what? it worked.

    edit: btw i don't expect anyone to try a test compile before they answer every question, but if you're not quite sure wth you are doing, then, yeah.

    What?
    Assume that MaxX = MaxY = 8, then the available memory in the array is 8 * 8 = 64.
    X and Y will range from 0 - 7.
    Assuming the "worst-case", that X and Y is as large as they can be, then my formula will produce the number 7 + (7 * 8) = 63, which is within the bounds (the last element in fact).

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    moi
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    Originally posted by Magos
    What?
    What? It doesn't work! That's what.

    edit: apparently the person who asked this question wrote two threads about it (not a good idea), and i'm interchanging information between the two threads. the reason your way doesnt work here is because of the way he's using the array.
    Originally posted by monkey_C
    OK, wDeck was originally declared in main() as

    int deck [4] [13] = {0};

    and was passed into the function containing my problematic line as

    const int wDeck[][13]

    but I still don't see how that's affecting my code. I think I've just been staring at the same line for too long.
    check out illegal operand for the whole dealie. because he's passing it as a two dimensional array, trying to access it as a one dimensional array wont work unless you something like
    (&wDeck[0][0])[X + (Y * MaxX)]

    or pass a *int in the first place, or do something like hammer outlined. but this is all very redundant and useless. monkeyc, care to elaborate why it must be this way?
    Last edited by moi; 09-13-2002 at 03:44 AM.
    hello, internet!

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    Registered User The Dog's Avatar
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    Try this:

    Code:
    myType  wDeck[50][50];    //for arguments sake
    myType* temp;
    
    temp = (wDeck + (y * MaxX + x)); //MaxX is a constant
    y is the first subscript and x is the second.

    so to access element wDeck[1][10]; which is the 61st element, y would be 50, which gives us 50, plus x which is 10, gives us 60,
    added to wDeck reveals the 61st element.

    I haven't tried it but it look's sound to me.
    Last edited by The Dog; 09-13-2002 at 03:44 AM.

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