simple question in arrays

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  1. #1
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    simple question in arrays

    What does it mean when passing an array in this way :

    key[16];
    j+=0;
    k+=0;

    getArray(key + j, key + j + k, k, k);


    is that shifting or something similar ?

  2. #2
    SAMARAS std10093's Avatar
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    Try to print the first element of the 1st argument and of the second argument inside the function. Before calling the function initialize the key array to something like 0,1,2,3,...,16 or something like that. Then remember how pointers and arrays are connected.

    And do not forget, always post your code in code tags!!!!
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  3. #3
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    No, it is not "shifting".

    Assuming array_name is an array of N elements, and i is an integral value,such as
    Code:
        float key[N];   /* float type picked at random */
        int i;
    then the notation "array_name + i" is a pointer with the value equal to "&array_name[i]".

    Any attempt to use that pointer (e.g. inside your function) will yield undefined behaviour unless i is a valid index (for an array of N elements, i is only a valid index if it is between 0 and N-1).
    Right 98% of the time, and don't care about the other 3%.

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    Quote Originally Posted by abood1190 View Post
    What does it mean when passing an array in this way :
    getArray(key + j, key + j + k, k, k);
    It's not passing an array, it's passing two pointers to two locations in the array and then passing the same integer twice. As mentioned above, it's the same as:

    getArray(&key[j], &key[j+k], k, k);

  5. #5
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    your comments are very helpful guyz

    I notice from the output that it changes the result of some elements

    lets say this code :

    Code:
    key[16];
    j+=0;
    k+=0;
    
    getArray(key + j, key + j + k, k, k);



    the + will change 1 value of the array key[] from the right when j is 1 to a weird value looks like an address and when it is -1 that will change 1 value from the left of the array !! why is that
    behavior?
    Last edited by abood1190; 05-12-2013 at 09:17 AM.

  6. #6
    Kiss the monkey. CodeMonkey's Avatar
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    Please provide a minimal complete program, its ouput, and your question.
    "If you tell the truth, you don't have to remember anything"
    -Mark Twain

  7. #7
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    Quote Originally Posted by CodeMonkey View Post
    Please provide a minimal complete program, its ouput, and your question.

    Code :


    Code:
    #include <conio.h>
    #include <stdio.h>
    
    
    
    
    void getArray( int key[] ){
       int i;  
      for ( i=0 ; i<6 ; i++){
          printf(" %d ",key[i]);}     
         
         }
    
    
    
    
    main()
    {
          
       int i;      
    int array[]={1,2,3,4,5,6};
    getArray(array+1);
     
        getch();
    }

    Output :

    2 3 4 5 6 2293616

  8. #8
    C++ Witch laserlight's Avatar
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    You are accessing the array out of bounds because getArray accesses key[5], which corresponds to array[6], which does not exist.
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    Look up a C++ Reference and learn How To Ask Questions The Smart Way

  9. #9
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    Quote Originally Posted by laserlight View Post
    You are accessing the array out of bounds because getArray accesses key[5], which corresponds to array[6], which does not exist.
    Sorry, i didn't understand

  10. #10
    C++ Witch laserlight's Avatar
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    Compile and run this program:
    Code:
    #include <stdio.h>
    
    void printArray(int numbers[], int size)
    {
        int i;
        for (i = 0; i < size; i++)
        {
            printf("%d ", numbers[i]);
        }
    }
    
    int main(void)
    {
        int array[] = {1, 2, 3, 4, 5, 6, 7};
        printArray(array + 1, 6);
    
        return 0;
    }
    C + C++ Compiler: MinGW port of GCC
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