Multidimensional arrays

This is a discussion on Multidimensional arrays within the C++ Programming forums, part of the General Programming Boards category; Hallo, I am trying to understand how multidimensional arrays work but can't seem to figure it out. I would like ...

  1. #1
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    Hallo, I am trying to understand how multidimensional arrays work but can't seem to figure it out. I would like help in understanding them. Yeah googled already but what I have seen so far seem to say "a multidimensional is an array of an array" which doesn't help much in understanding. I have a code here and its output. I would like someone to explain it to me the outcome well. Thanks in advance.

    Code:
    #include <iostream>
    using namespace std;
    intmain()
    {
    intar[]={123,456,789};
    intind[]={2,1,2,0};
    intk;
    for (k=0;k<4;k=k+1) {
    cout<< ar[ind[k]];
    }
    return 0;
    }
    Output: 789456789123

    OK I think I figure it out.


    OK the loop produces the values 0, 1, 2 and 3. Putting this in the array the statement becomes:

    cout<< ar[ind[0]]; and so on till array 3.

    From here then it is easier. Because ind[0] = 2, so it becomes array[2]. Although I understand this but intar[] has only 3 values while ind has 4, so when intar runs out of values to loop over, what is supposed to happen? Does it go back to zero and start it all over again or?
    Last edited by Dontgiveup; 03-25-2011 at 01:24 AM.

  2. #2
    Programming King Mr.777's Avatar
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    First, these are not multidimensional arrays but only single arrays.
    when intar runs out of values to loop over, what is supposed to happen?
    Definiterly, crash..... Boooooooooommmmmmmm!!!
    No it will not go back to zero, a runtime error.
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  3. #3
    C++まいる!Cをこわせ! Elysia's Avatar
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    Erm, nothing of the sort.
    It doesn't matter that ind has more indices than array. The simple reason is that ind stores the indices in array that you're going to access. So ind can be of infinite length and it will all be well so long as the contents of ind is 0 < i < length of array - 1.
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    Thank you Elysia and Mr.777. I now understood it. So you basically output the values in ar[0],ar[1],ar[2],and finally again ar[0]. Ooh and I thought it was a multidimensional array.

  5. #5
    Registered User C_ntua's Avatar
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    Quote Originally Posted by Dontgiveup View Post
    Thank you Elysia and Mr.777. I now understood it. So you basically output the values in ar[0],ar[1],ar[2],and finally again ar[0]. Ooh and I thought it was a multidimensional array.
    It actually outputs ar[2], ar[1], ar[2], ar[0] as you can see from the result.

    You can always take it step by step and figure it out.
    1st loop: k=0
    ar[ind[k]] = ar[ind[0]]
    you know that ind[0] = 2
    ar[ind[0]] = ar[2]
    you know that ar[2] = 789 thus
    ar[ind[k]] = 789
    which is what you get

    2nd loop: k=1
    etc etc

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