need help with passing an array in a recursive (merge sort) function

[pacman529]

my assignment is to get a function to merge sort data. we can use either arrays or linked lists as our data structure, and i picked arrays. here is my function:

void merge_sort(int *list[], int listlength)
{
      //if the list only has one item, return the list to the previous function
      if (listlength<=1)
      {
         return;
      }
      
      
      //initalize the lists that are going to be used
      int left[listlength/2];
      int leftlength = listlength/2;
      int right[listlength-listlength/2];
      int rightlength = listlength-listlength/2;
      int result[listlength];
      
      
      //split the list into two halves to be merge_sorted
      for (int i=0; i<=listlength/2; i++)
      {
          left [i]= *list [i];
      }
      int j=0;
      for (int i=listlength/2+1; i<=listlength; i++)
      {
          right [j]= *list [i];
          j++;
      }
      
      
      //here we merge_sort each half
      merge_sort(*left[], leftlength);
      merge_sort(&right[], rightlength);
      
      
      //then merge the two sides together!
      merge(left[], right[], &result[], leftlength, rightlength);
}

for my last 3 lines of code, for the parts where there is '[]', it says "expected primary-expression before ']' token"

if i take out the brackets, it says: "cannot convert `int (*)[((unsigned int)((int)(listlength / 2)))]' to `int**' for argument `1' to `void merge_sort(int**, int)'"

can anyone please help me with this? i feel like i'm so close right now.

[Mathhead200]

Why does this function take an array of int* types?

[pacman529]

what do you mean? i thought i had to have the * in there to make it pass by reference? to be honest i am not so sure if i am using all these pointers and what not correctly. i hate using pointers.

[pacman529]

i was trying to use this example from wikipedia:
http://en.wikipedia.org/wiki/Pass-by-reference

void Modify(int p, int * q, int * o)
{
    p = 27; // passed by value - only the local parameter is modified
    *q = 27; // passed by value or reference, check call site to determine which
    *o = 27; // passed by value or reference, check call site to determine which
}
int main()
{
    int a = 1;
    int b = 1;
    int x = 1;
    int * c = &x;
    Modify(a, &b, c);   // a is passed by value, b is passed by reference by creating a pointer,
                        // c is a pointer passed by value
    // b and x are changed
    return(0);
}

[pacman529]

can anyone help?

[rwan]

In your function header, you have

void merge_sort(int *list[], int listlength)

The first argument means a pointer to an array. Loosely speaking (someone else will have to explain to you the difference...), it is similar to: int **list, or an array of int* types.

When you pass an array to a function, you are already passing a pointer -- you're passing a pointer to the beginning of the array. So, you don't need the extra *.

Personally, I still get all the * and [] confused from time to time, especially when I'm lacking sleep. :-) Try to step back from mergesort and see if you can create an array of integers in one function and pass it to another function to print it out...

[pacman529]

finally got it! got rid of all the *'s and &'s and it ran but didn't work, then i just had to change "result" in line 37 to "list" so it would actually effect the damn list.