Thread: It is just not clicking in my head (Output an array via pointer in reverse)

  1. #1
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    It is just not clicking in my head (Output an array via pointer in reverse)

    So this is one of thoose things that is not clicking in my head.

    I am trying to write a function using "pointer notation" that will write out the elements of an array of int in reverse order. I know this has to be done via a for loop but I am a little lost when it comes to the "pointer notation". When assinging the address of a pointer to an array it assigns it to the first element [0] correct? Anyways I would appreciate it if someone could offer up and example.

    Thanks

    Chad

  2. #2
    and the hat of int overfl Salem's Avatar
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    for ( p = &array[n-1] ; p >= array ; p-- )
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    Quote Originally Posted by Salem
    for ( p = &array[n-1] ; p >= array ; p-- )
    What are the declarations in this? Is p the pointer?

    So p = the address of the array, correct?

    What is n? The element of the array?

    Why n - 1? This has something to do with the fact that arrays actually start at 0 correct?


    Thanks

    Chad

  4. #4
    and the hat of int overfl Salem's Avatar
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    So p = the address of the array, correct?
    p is a pointer to an element of the array. If you have T array[n] then it's T *p
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.

  5. #5
    Frequently Quite Prolix dwks's Avatar
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    Why n - 1? This has something to do with the fact that arrays actually start at 0 correct?
    Exactly:
    Code:
    int a[10];
    /* printf("%i\n", a[10]); /* out of bounds */
    printf("%i\n", a[9]); /* 9 is the last element . . . n (10) - 1 */
    dwk

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    What are the declarations in this?
    They were left out for brevity.

    n=size of the array. If you have the array:
    Code:
    int myArray[] = {10, 20, 30};
    the size of the array is 3 but the valid index numbers are:

    myArray[0] = 10
    myArray[1] = 20
    myArray[2] = 30

    An array name is like a pointer to the first element. So, you can set a pointer to the first element like this:
    Code:
    int* p = myArray;
    cout<<*p<<endl; //10
    Or, you can set the pointer to point to other elements of the array:
    Code:
    p = &myArray[2]; //"p is equal to the address of myArray[2]"
    cout<<*p<<endl; //30
    Pointer arithmetic allows you to move the pointer along the array with the increment operator(++) or the decrement operator(--). Since you want to output the elements in reverse order, setting a pointer to the end of the array, and then decrementing that pointer everytime through a for-loop to move it along the array seems like a good approach.
    Last edited by 7stud; 10-21-2005 at 02:17 PM.

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